A/N: Somewhere along the line, someone in the First Order figured out that leaving a lot of abandoned but functional factories behind them was a bad idea. As we saw in A New Hope, Empire Strikes Back, and The Last Jedi, as well as the Phasma book.
The Otomok system contained the planets Hays Major (barely habitable) and Hays Minor (ice world). The latter was the homeworld of Rose and Paige Tico. Major export: crystalline ore.
Hux to Rose, TLJ deleted scene, as he picks up her pendant, which is a stylized symbol of her homeworld: "The Otomok system? That brings back memories."
Wookieepedia:
The First Order forced her people to mine their planet's resources to feed their war machine, then shelled them to test the results. Having lost everything they had to the First Order, Rose and her sister joined the Resistance to avenge their homeworld.
Also from Wookieepedia:
Hays Minor was a planet in the Otomok system that was the homeworld of Rose and Paige Tico. Prior to the pair joining the Resistance, the First Order used the world to test weapons and steal children to become stormtroopers.
Five ships loomed above the scintillating white and dull tan of the landscape of Hays Minor. Hux stood on the bridge of the Finalizer, looking down at it. He could just make out the darker smudges that constituted the mining facilities and the cities that had grown up around them. "Are the harvest ships clear?"
"Yes sir," Mitaka confirmed from behind him.
"And the evacuation complete?"
"Yes sir."
"Well then. Seeing as the mining company has signed off on surrendering their claim to all remaining equipment and facilities, we can begin demolitions." He turned to Mitaka with a smile. "And, of course, the weapons testing. I am most interested to see how these new dreadnoughts perform against ground installations."
In the later stages of the Supremacy's construction, Drewmill's group had begun a new wave of ships – small in number, but exceptionally heavy in firepower. They were designed for planetary bombardment and the overwhelming of defense networks, not for interspace battles. They would be useful in retaking any New Republic worlds too valuable to destroy outright but too fortified to take otherwise.
"Yes sir," Mitaka said. "Shall I signal the barrage?"
"Oh, I suppose so. But first get me a visual on the initial target. Sephis Major, was it?"
Mitaka checked his notes. "Um, Sebris Alpha."
"Very well," he said dismissively. It was about the same thing and about to be rubble. Everyone who called it anything else was gone. "I want to see this in real-time. We might want to make adjustments to the targeting pattern on the other installations."
Mitaka set up a nearby screen to show the best resolution their scanners could provide. It was still a bit grainy. Hux decided to watch the first few volleys from where he was at, looking out the forward viewport. His hands were tucked behind his back.
"Fire at will," he said over his shoulder, listening as Mitaka relayed the signal to the two forbidding-looking dreadnoughts accompanying their three star destroyers. In a few moments, streaks of light showed the path of the plasma bolts fired from the accompanying vessels – one dreadnought on this target, the other on a second on the southern hemisphere.
Hux muttered to himself, "It might be worthwhile to do a bombardment with the destroyers first on one of the other facilities, just for comparison."
"Sir?" Mitaka asked.
"Nothing," Hux said. Silent explosions flared on the surface of the planet. They weren't as large as he'd expected. Clearly, things had been hit and were blowing up, but he'd been expecting bigger. His sense of perspective was skewed from watching old holos of Death Star superlasers against Jedha and Scarif.
He supposed the dreadnought's bolts lost a lot of power punching through the atmosphere as they did. That was good to know. There were some things that were impossible to visualize well from looking at the numbers. He moved over to the scanners to get a better look.
The destruction was clearer this way. He moved the viewing area across the target zone. Just outside the area, he could see small, dark dots moving in what was left of the streets. "That's a lot of movement." He narrowed his eyes and leaned closer. "Are those people or droids?"
Mitaka came over and stood next to him. Both of them stared at the screen, trying to make sense of what they were seeing. Like imperial weapons and the Republic before, First Order weapons tended to have specific radii of effect, with (relatively) little damage outside of it. The idea was that area of effect weapons should effect their targets only and nothing else. Superlasers were an exception, which was part of why their existence was considered an abomination by itself, in the opinion of most of the galaxy.
"Uh … I don't know," Mitaka said. "Wouldn't the mining company have taken their droids with them?"
"Of course they would have," Hux said. "Droids are valuable equipment. People? Not so much." He gave Mitaka a sharp look. "I asked you if the evacuation was complete."
"Well, it was. Sir." The lieutenant retreated to his workstation, checking the reports. "Colonel Kaplan said it was. Here, he attached the mining company's report that it was."
Hux imagined what it must be like to be down there, with a rain of destruction coming from above. The station was already functionally obliterated, but at least he could do something before the dreadnoughts moved on to their other targets. "Stop the bombardment."
"Yes sir."
Hux knew where this report was going. He sat behind his desk, tired already. He looked up at the colonel with an upset, long-suffering expression. "What you're telling me is that the mining company fired everyone they didn't want to bother evacuating. Is that it?"
"I suppose so, sir. Yes."
"And so the bases we're supposed to destroy, to prevent infestation by pirates, rebels, organized crime, or whatever, are now already infested with the very workers who were left behind." He leaned back.
"Yes sir."
"To some extent, this is exactly why we're supposed to destroy these things – so that we don't leave a trail of struggling enterprises behind us, ripe for conversion into Rebel bases of operation. The only reason the corporation pulled out was because it's no longer economically viable. There may be enough left to scratch by on, but these things are magnets for illicit activity." Hux shook his head. "Did the harvest ships at least collect the children?"
"Some of them, sir."
"Some? Not all?"
"It's voluntary surrender only, sir."
"Yes, I know it's voluntary surrender, you idiot. I was there when the policy was drafted! But they didn't know we were going to shell them! They stayed because they thought the mining infrastructure would still be there for them – their jobs, their homes. Our orders are to destroy it. They won't have anything after we're done!" Hux gestured furiously from his seat.
Chastised, the colonel looked back and forth on the floor before agreeing, "Yes sir."
Hux scoffed, sighed, and looked away. "How many people are down there?" he snapped. If he evacuated the adults, they'd be enrolled as slaves. Except in very rare cases, that was all they'd ever be in the First Order. The Order had no broad-based social support system to handle adult refugees of uncertain loyalty. He was sure Snoke wouldn't stand for him transporting them anywhere else. Snoke barely allowed him to take in the children.
"I don't know sir. Our orders were- my orders were clear." He sounded apologetic.
"Yes," Hux said in a calm aside intended to sooth the man, "I know they were. I am not criticizing your conduct. You did what you were told to do." He put a hand over his mouth for a long moment, then dropped it to the desk. However disturbing the situation was, this wasn't his mission. "My orders are also clear. I want you to mobilize every combat pilot we have on shift. You can characterize it as another weapons test. I want their squadrons to strafe the mining facilities-"
"Standard armaments won't be effect-"
"I know. Be quiet. That's the point. I want them to strafe every factory we have listed for demolition. No shots at civilians. Run them out of the buildings. Let them flee to the residential sector. As soon as the squadrons are out of the way and we have visual confirmation from the pilots that the target zone is clear, we'll start the bombardment again. In the meantime, I will have the targeting crews tighten the spread so all we're hitting are the mining facilities. It's all I can think of. Do you have any better ideas? Or other ideas at all?"
"No … No sir."
"We'll need to send harvest ships back in a few months for whatever children are still here. The parents will change their minds after they've exhausted their food supply. The slave traders will be by after that for whoever is left."
"They might evacuate themselves in the meantime."
"True. If they do, then good for them. Not everyone has access to that. We'll send the ships back anyway."
A/N: The weapons thing is an attempt to give in-universe logic to a movie convention. In canon, grenades, bombs, mortars, and shells tend to kill everyone in a certain area, and no one outside it. There's a loud bang and maybe a little concussive force, but you don't get the blast effects these things cause in the real world, where they blow out ear drums, rupture eyes, collapse lungs, hemorrhage delicate bodily structures, and give concussions. To explain this, I say the galactic weapons have been designed to be all-or-nothing, just like we see in the movies. They either kill people or they don't. To do otherwise is considered barbaric. As Obi-Wan said, "An elegant weapon for a more civilized age."
It should be noted that all uses of superlasers (Death Star) we've seen in canon conform to the 'all or nothing' principle. Both Scarif and Jedha were surrounded by a basically unpopulated area (ocean for Scarif, desert for Jedha) and only those people in the intentional target area died. Same goes for Alderaan and the Hosnian system, if you accept that the intention was to kill everyone on the planet.