Difference is other orgs have parameters in place to decide championship matches: playoffs, heats, tourneys, etc.
Ufc, boxing does not. So when the match makers put on a fight I'm sure they do so with the titles integrity in mind, but you bet your ass that there are others in the room pushing PPV buys.
playoffs, heats, and tourneys are impossible under the unified rules. they really only work over a couple of days, not a few years. look at the strikeforce tourney for why.