In advertising, sex sells. In MMA, rivalries sell.
Looking back at some of the greatest fights in MMA history, one will notice that the majority of them involve some legitimate dislike between the fighters. Even if it is just pre-fight hype, the belief that two fighters hate each other is a successful formula for gaining fan interest.
There are often two kinds of rivalries that emerge in the ultra-competitive sport of MMA; those that come about from mutual hatred and the competitive kind. The rivalries that evolve as a result of two guys not liking each other is pretty self explanatory.
The "competitive rivalry" is one that forms due to two guys being on a virtual collision course as a result of their performances inside the cage (or ring). These bouts don't need bad blood for us to tune in as the competitive nature of two elite athletes tends to be more than enough to gain our interests.
No matter what drew you into these rivalries, there's no denying that when the fighters finally got to settle their differences, we all tuned in.