I cannot explain why most people who enter MMA tournaments with Wing Chun get demolished.
If they are it's because no fighter in MMA is a one style fighter, all good fighters have taken techniques from as many styles as they need to.
I get rather tired of these arguments that say a particular style is no good in MMA, it's nonsense because the very name gives it away MIXED martial arts, so why do the ignorant keep going on about Wing Chun/Aikido/karate etc etc being no good? There are techniques in all these styles that work along when put into the mix, to be honest there shouldn't be much to differentiate styles when you watch a fighter. He doesn't do one style for kicks, another for strikes and yet another for takedowns, they should all be a smooth mix flowing from one move to the next, a good fighter is always a couple of moves ahead anyway.
Anyway I thought you'd like this, Sami Berik from Wing Chun ( with a very young Grant Waterman reffing)