The win bonus in MMA is a double-edged sword that improves fights as much as it hurts them, removing some of the chances that fighters might otherwise take. It can lead to better fights, though it can also lead to slow-paced matches with neither fighter trying to finish the other.
Fighters should aim to make as much money as possible whenever they step into the cage. They have a very limited window in which to make money and a win bonus nets them a healthier profit. It also makes some fighters come up with a safer game plan.
This is most seen in wrestlers who will control their opponent for three rounds, but not try to finish them off. Fighters like Jon Fitch or Nik Lentz can grind decisions and rack up a decent paycheck that way.
The only problem is it makes the sport unwatchable for the casual fan.
As much as MMA is supported by the diehard faithfuls that have populated it since its beginning, it is the masses that really fund those that participate in it. They want to be entertained and skill comes second.
That doesn't mean that MMA companies should cater to them or sell out, it just means that promoters need to be prepared for when fighters choose to win over looking good. In that sense, win bonuses cause a lot of problems.
But for every issue that there is with win bonuses, there is a poorer option in their place.
Boxing has never had win bonuses and while that means a fighter's paycheck won't fluctuate at any point, it also means that fans might see some competitors phone it in. It happened when Nonito Donaire fought Omar Narvaez on HBO. The fight was supposed to be a great one, but it turned into Narvaez running away for most of the fight.
Because he had been paid in advance and there was no way that the promoter could lessen his fee. He could do whatever he wanted as long as he didn't throw the fight purposely and he showed up.
MMA stops fighters from being able to do this by making winning something that is financially rewarding. There might be some fighters who take this to extremes and choose to not engage in any risks while in the fight.
This seems oxymoronic, but more and more fighters are doing it.
They shouldn't be blamed for it as they need to make money and there isn't much promoters can do to change policy without making it worse.
Some companies like the UFC award bonuses for exciting finishes which cuts down on any possible monotony, but it is something that will always exist. Fighting cautiously for win money is something that is unique to MMA, but nothing that will ruin the sport in the long-run.
And it's better then the alternative.