For all the so called kung fu martial artists out there...can anyone give me an honest answer???

By now I am sure most of you have heard enough stories about how skillful and incredible some kung fu masters are and that kung fu skills can over come external forces coming from bigger opponents etc...you get my point. so my question is for all the greatest kung fu masters and martial artists from all over the world including yourself, why haven't any kung fu man (mantis, tai chi, hung gar, shaolin, choy lay fut, wing chun, xing yi, ba gua, jkd whatever etc...) able to use his skills in the MMA (Mixed Martial Arts tournament) or the Ultimate Fighting Champion??? Is it because of the size, strength, speed or fear or lack of skills or what? Please if anyone can give me an honest answer I would appreciated. And I am sure some of you martial artists out there would like to know too....thanks you for your time and honesty!

Ironcu.