Millions? These are contractors and still have to pay more taxes than normal, in that it isn't already taken from your check. Not to mention to pay for training and coaches flying out and hotel/food/etc. Not sure how the health insurance is for contractors but it can't be that great compared to an employees health insurance, not to mention 401k or whatever for retirement.
Then throw in the fact that these UFC fighters are supposed to be top athletes in the world, yet they try to live like the other top athletes who actually make money. Look at conor having to rent out yachts and cars to drive. The UFC didn't do these guys any favors by giving them only around 15% of the revenue if that. Not to mention killing their sponsors for that rebook coupons.