Look at it from an economic perspective. The UFC pays Sean the same whether he's fighting in a number 1 contender fight or crushing a bum. Economically and rationally, why would someone do a harder job for the same pay? That's an incentive problem, and the UFC controls pay structure and rankings. It's more the promoter to blame than fighters.No, they don't at all. Fans were and at O'Malley for saying he'd rather fight bums than killers, but there's an inherent incentive for any fighter to feel that way.
I've said this over and over again since people ignore this, but during the golden ages of boxing that people like to talk about, where the best fought the best, boxers were compensated as well or better than Conor McGregor. They were economically incentivized to fight the best. It's not a panacea, but economic incentives matter a lot.