Sam and Dean don't have a childhood documented in photographs. Hell, they don't have a shirt from five years ago that's not at the bottom of a trash bag covered in blood. With everything that comes and goes, they have three boomerangs. Each other. Hunting. The Impala.
Sam left for college. New start, his choice. Dean was left with his car, man he loved saying that, and the family business. With his Dad, by himself. It wasn't perfect. He missed his baby brother and he would never not be responsible for that kid, but Sammy walked away on his own accord. He wanted this, so Dean wouldn't bother him.
When Dean got dragged to hell, he had nothing. He was merely an animal by the time he emerged from his not-so-eternal damnation.
Sam survived four months without his older brother. He drove the car, tried to deal, and even unsealed the Devil's Gate. Dean was still in the pit. Sam in his grief found something that helped. Demon blood. It sounded evil, but how bad could it be? It saved lives. The tang in him mouth wasn't a horrid one.
Sammy took the swan dive into Hell, Center Of. He stopped the world from ending. He saved the whole friggin world, and they thank him by locking his ass in the cage with Satin himself, throwing away the key.
Dean let that happen. He couldn't take that back, so he found the apple pie and cut himself a slice. Sam overcame the devil. Yippee, here's a fork.
He had Lisa. He had Ben. He had his car. On the nights he didn't wake Lisa with his screams, he stumbled to the garage and sat in the passenger's seat. Here, Sammy, you drive a while.
The impala was theirs. It was the car they learned to drive. Dean once rebuilt her bottom up, the trunk was big enough to fit a body, and that could be pretty damn useful.
"You know, it's bad enough that they're ganking people, wearing our mugs, but now this? Have us driving around in this... this caboodle while Baby's on lockdown."
Sam sighed. He agreed. The impala helped him overcome the devil for Christ's sake, but complaining would get them no where. "It's temporary, Dean."
But if they could take away their home, what else were the Leviathan capable of?
Dean had hunting on his mind, a knife in hand. Purgatory was an endless hunt. He'd focus on the that. He took it day by day, survived the on slaughter and kept on the lookout for Cas. If nothing else, he had the hunt in its purest form.
Sam had no one. Dean and Cas were vanished. Bobby was dead, Crowley had Kevin. "Without a master plan, the Levis are just another monster. Hard to stomp, sure, but you love a challenge. Your job is to keep them from organizing." Ha. Not this time, Crowley.
As far as he was concerned, everyone was dead. Hunting had his whole family ganked, all his friends. There were other hunters out there. He just saved the world, let them deal with the aftermath.
Sam did the only thing he could. He fixed up the impala and drove. If nothing else, he had home on wheels.
Only in hell were they without a constant to cling to.