Han may have been simply caught up in helping find a new base and relocating to Hoth. He also could have been doing missions for the Rebellion, none of which got him close enough to pay Jabba in person. I guess there’s no paypal in a Galaxy Far Far Away. 😉
Han may have also felt “safe” from Jabba’s reach hanging out with the rebels, until the bounty hunter encounter.
There’s also the question of what happened to the money between ESB and Jedi.