Nothing generates interest like a little bit of controversy. Sometimes it happens by accident, but more often it is a result of two fighters simply not liking each other and wanting to get under the other's skin.
Fans love it when two fighters genuinely dislike each other. It creates for some good back stories to the actual fight. It can even make some of the mid-card fights overshadow the actual main events.
Not all fighters create controversy by simple trash talk. The athletes have found numerous ways to create a stir that causes MMA fans to head to the nearest computer. Nevertheless, these fighters create controversy and with it, an overwhelming interest in their careers.