Fighter pay is extremely overrated in terms of attracting high-end athletes.
Would higher pay attract more wrestlers, kickboxers, and bjj players to mma? Yes. But it wouldn't make a difference in terms of athletes who "choose" to play soccer, basketball, football, baseball, hockey, etc. People in those team sports started playing when they were very young. Children don't start playing basketball because NBA players make a lot of money; generally speaking, they play the sports that are baked into the fabric of the community they're in.
If we're talking about attracting LeBron James to mma, you don't throw a bunch of money at him when he's 18. By that point, he's already firmly established in his sporting trajectory. You have to increase participation by kids from a young age--which is obviously a very hard sell for most parents.