There are entire lines of trendy clothing (and douchey t-shirts) dedicated to MMA. People have "Tapout" stickers on their cars.
I think that this is just a difference in culture between MMA and other sports. Individual figures aren't really what's touted in MMA. You aren't going to find many people wearing a Randy Couture shirt, like you'd see someone wear Dolphin stuff. Instead, it's about gyms and clothing lines. So, if you're a fan of Uriah Faber, you're probably also a fan of his training team and the other guys that fight at his gym. They'll likely have similar styles and mindset. And they are represented by "Team Alpha Male", so you might wear their clothing line. That's why you see Tapout. It's representative of the sport as a whole, not just the individual.
It's just a result of not having a traditional "team" structure with logos and stuff, like you see in the NFL.