What is the deal with the ineffective rubber guard in mma?

If you have heard what I have heard about the rubber guard then you have heard that it is the future of Jiu-jitsu in maa. I plan on mastering a few simpler parts the ground game before I start toying around it but have you been watching the UfC or the Wec as of late. Guy after poor guy is on his back trying to make use of the rubber guard but nothing comes of it. They throw there leg up towards the head and grab on and then either hold it for a little and let go or let it go virtually seconds after they get it on. Why is that. Frankly Jiu-jitsu in general has seemed to take a back seat to wrestlers in the ufc which I think is testiment to the fact that any good jiu-jitsu guy these days has got to master striking and being on his back. Any one have anything to say?