Really? Pretty sure Roy Jones fought a fireman on HBO.
And that goes for a lot of fringe contenders in boxing.
I'd imagine similar is the case with really bad tennis players.
Pretty much any team sport though is going to pay well, and even if it doesn't, like low leagues of soccer, football and baseball, typically your opportunity costs are a lot lower. But it's also apples to oranges...in the case of the NFL and other team sports, you have an individual owner and organization that is trying to maximize your performance for HIM to win.
The promoter in individual sports is neutral and thus has no stake in your training or preparation for fights, nor the result.
Secondly, a lot of the times, the fascination with winning in team sports is both a business move, and just for the sake of fun and competition. A lot of the owners are absurdly rich...guys like Jerry Jones and such are likely richer than all of the UFC's assets combined. The Cowboys is as much a toy, and an obsession...a game....than an actual financial and business venture. Some of the newer owners only field teams as competitive s to not hurt their bottom line, but others don't really give a damn because this is just one of many investments they have millions of dollars tied up into...and generally it's going to be very profitable.
So in reality, you know a way you could increase fighter pay?
Have the UFC like the IFL where fighters are sponsored by multi-million/billion dollar owners and distribute the revenue that way...however to do that, you are going to need a shitton of TV revenue....which MMA just isn't generating right now.
Golf not so much though. Golf is awesome and anyone who makes the tour is living the dream.
I wish I could golf.