The problem with these last few epdisodes is that they were incredibly rushed. We can only guess what these people's motives were, as we certainly can't determine it from what was shown. That part about the guy whose brother was killed is pure insanity. Oh he killed my brother in cold blood, that's a man I want to put my life on the line for. If they'd put more time into these characters they might've built up some motivation, but at the same time 2 Governor centric episodes was already more than most of us could take. The writers created an terrible mess for themselves by not killing off the Governor last season and these last few episodes paid the price for it.
Thankfully, they cut their losses and the outcome is pretty positive. A few main characters dead, including the guy who's been the main villain for what seems like an eternity now. An most importantly, finally a change of scenery. We've got separated groups and everyone will be on the move for at least a while, so that's something to look forward to.