Using the head and clinching is kind of like flopping in basketball or football (soccer). People do it because they can get away with it. If refs didn't call them, or they would penalize them for it, it would stop.

Certain fighters use the head because it's effective and they never get called for it. I understand even though i disagree. So the fighter isn't the problem. The problem is that the refs aren't being told to crack down on it.