Most versions of Professional Wrestling are now billed (and operated) as "Sports Entertainment". As such, the story lines that you see are scripted. The matches generally script the winner (often with the "winning move/maneuver"). Additionally, a lot of the time, professional wrestlers do not go by their actual names, and the information about them is generally changed to fit the storyline or scripted background.
Add to this the fact that many times even the "goodness" or "badness" of a professional wrestler is manipulated and scripted, and you have a entertainment program that bases its actions as "sports". Think of professional wrestling as a "Sports Soap Opera".
MMA, on the other hand, is attempting to establish itself as a bone fide sport. As such, the outcome is not scripted. The crowd reaction of an MMA fighter is not necessarily manipulated or scripted. There is no choreography in MMA fighting (unlike professional wrestling).
That's the difference: one is sports entertainment programming, the other is 'simply' a sport. Hope that helps.