The Ultimate Fighting Championship has been growing at an astronomical rate ever since Dana White and the Fertitta brothers gained ownership and control. There were many landmark events in the sport's growth, but fighter bonuses were pivotal in turning the company around.
Boxing has been losing some of its fan base with the way that top fighters are performing. I love boxing, and enjoy watching a technical match, but I can see how the casual fan would get bored. Boxing isn't delivering slugfests and brutal knockouts like it used to.
The UFC recognized this problem with combat sports, and sought to change the stigma. Their goal was to appeal to fans who are not as intense following the sport.
Bonuses were the program that they put in place to try and change the pace of fights. They have 'fight of the night', 'knockout of the night', and 'submission of the night'. They've been a massive success.
Legally, the UFC isn't allowed to tell fighters how to fight.
They found their way around that though, with bonuses. Many undercard fighters will never get a chance to get a proper UFC paycheck. They make very little money for the body of work that they put in.
Rising the UFC ranks is hard.
They only sign fighters who have winning records, and have fought in smaller promotions. Even stringing together a bunch of victories and getting on the main card won't guarantee you a six-figure paycheck.
Most guys will get cut, and never get more than three fights. Going for a crazy submission, knockout or just fighting their heart out with an opponent could multiply their paychecks exponentially.
This goes back to the UFC vs. boxing argument. The UFC tries to make every fight entertaining. Boxing tries to save money on undercard fights, as fans usually only care about the high-profile main event.
The skill level of the guys at the bottom of the undercard in both sports are similar, but the UFC has managed to make their guys fight a whole lot harder.
The UFC is still growing, and boxing is losing its fan base. Fight bonuses are undoubtedly one of the reasons this is happening.