In many places, the league or head of the officials organization reviews game tapes looking for missed/blown/incorrect calls and give grades to individual officials and officiating crews based on what percentage of calls they got right.

Officials who don't score well don't get assigned important games and don't get invited back next year, so there actually is a significant self-interest in calling a fair game (because if you don't, you're out of a job and you'll be back doing high school games before long).

But if it's easier to think that they are all just a bunch of cheaters taking bribes to throw games for their conference, just keep on believing that.