After coming out of the movie theaters, this started circulating in my brain. It's short, pointless probably, but still something I wanted to write. Moves a little quickly, so I apologize for that. Also, spoilers at the end for Transformers: Age of Extinction, so be prepared if you haven't seen the movie yet.
Earth had never been Ratchet's home.
Optimus had called Earth their new home after arriving on it per Bumblebee's radio transmission. They swore to protect the Earth from Megatron and the Decepticons, to save the Earth from the fate Cybertron had been given.
But Earth had never been Ratchet's home.
His opinions on the humans had been rather iffy. While Sam and the soldiers he fought alongside were acceptable to him, the human race as a whole was undesirable to Ratchet. They were primitive and violent, and were better off dead. But he was an Autobot, and it was their job to protect the weaker beings from the Decepticons.
Even when N.E.S.T. was formed and the Autobots worked with humans on a more one-on-one basis, Ratchet's opinion on the humans hardly changed. Even though the handful of humans he dealt with were respectable, humanity was still a force of danger to the Autobots, because Optimus would not condone the death of humans by their servos.
When Optimus died, Ratchet wanted to leave the Earth. Earth had been bad news for them since the start: Jazz was killed, they were basically at the beck-and-call of the government, many of their Autobot companions were killed in the campaign to protect Earth, and then Optimus was dead. There was nothing left for them, except Optimus' desire to protect the Earth. It was a miracle that Optimus was brought back to life, and so their continuous watch over the planet that barely knew they existed continued, even though Ratchet wanted to leave while the getting was good.
The human's betrayal only continued, from the President ordering their removal from Earth (which had been a trap; thank Primus for Optimus' determination to protect Earth that he disregarded this order), to their attempted destruction only a year after they saved the Earth at Chicago. After the second betrayal by the human government they had been protecting, Optimus had the remaining Autobots separate and retreat, and to break all contact with humans.
For years, Ratchet had been on the run; never staying in one place for too long, in case the humans found him. He had no radio contact with his fellow Autobots, and it had killed him not knowing whether or not Optimus and the others were alive or dead, but he followed his leader's orders without question.
After the years of being on the run, he was discovered on a steamboat he had taken refuge in. He didn't fire at the humans when they came for him; he ran, but was stopped before he could outrun them. He tried pleading with them, but they wouldn't hear it. He tried fighting back, but they had an ally on their side that incapacitated Ratchet: Lockdown.
The mercenary wanted Optimus Prime, even offered Ratchet a deal for the information; the chance to live if Ratchet told him where Optimus was. Ratchet knew Lockdown wouldn't made good on his deal; even if Ratchet gave up the location of his leader, Lockdown would kill him, or give him to the humans to be killed. But Ratchet would never give up Optimus' location; his loyalty wasn't with the humans or the Earth, but it was with Optimus, and he would rather die than hand over his leader to either mercenary or humans. And he would do just that.
Earth wasn't Ratchet's home, and the medic officer couldn't deny he wasn't happy he would be finished with the Earth for good.