In all fairness, GSP would probably be teaching karate at the local boys club if Dana never took over the UFC and made it into what it is today. Even single endorsement deal these guys have is because of the platform that the UFC provided...
That would be a fair argument if this was pro wrestling it isn't.
As much as it is entertainment, it's a competitive sport.
The UFC gets the big money because it's supposedly the most competitive league. Its competitive because they supposedly attract the best fighters.
If you don't pay enough to get the best fighters your league looses its value.
In the end the ufc gets away with it because it's a monopoly something no rational person should support.