Do you mean you hate only when they move down or generally changing weigh classes?
Do you disagree with Maia coming down to 170? Do you think that was a bad call he made?
What about Sonnen moving up?
Kind of what the other guy said, dropping down because they can't beat the champion. While Maia had a title shot at one point, his MW UFC career had become ropey, and a title shot never really seemed to be anywhere in the future. His body was more suited for WW anyways, and it's understandable that he realized that he could no longer compete at an elite level at MW and dropped down. Cain on the other hand CAN compete at an elite level, and the only reason he'd be dropping down would be if JDS was too good for him. If Demian Maia was turning away all challengers and constantly aiming for the title, I would have felt bad about him dropping, but unlike Cain he wasnt able to compete at that weight class. Cain's entire career is made up of smashing heavyweights, so he can compete as one of the best in the world and dropping down would be admitting that he isn't now, or will never be in his life, better than Junior Dos Santos, which is way too defeatist of an attitude for me to like the move (although he hasn't done anything so I'm not targeting him specifically).
Sonnen did the same in reverse. At LHW, Sonnen faced some much bigger and badder challenges than at MW, so his move isn't really taking the easy way out. He is facing someone who to me is an even more difficult challenge for him, Jon Jones, than the man he moved up from, Anderson Silva, so he is more accepting the losses and trying to carve out a more difficult route under the wall he faced at MW.