to find luke when he went missing on hoth?
Because he's a big pussy.
literally
A really big and hairy one at that!
Because it just would have looked silly seeing him riding a taun taun. Now Han riding on Chewie would have looked better. Gay but better.
Maybe because he was needed to work on the falcon more.
Didn't do a fucking good job, did he, GGO8?
Well to be fair neither Han or Chewie knew a part of the hyperdrive needed replaced. And even if they did know I doubt the rebels had one. Doesn't help he can't go to a civilized system due to the bounty on his head.