The simple point of the matter is if you bring something to the table (a major belt or big TV money or both) then the K brothers can and do pay well. If you're mandatory then at least you get the minimum cut (25-35% depending on sanctioning body).
If you're a nobody or a have-been, you have no belt and all you want is a voluntary chance to win the title and an easy pay-day then you get jack****
. You bring nothing to the table you get nothing. Simples.
It's like in the real world. If you're a homeless highschool-dropout you can't go asking around for a $250k annual salary job without getting laughed at