I think the primary problem is that guys are afraid to try new things or are quick to dismiss certain moves. It's not until someone really kicks ass with something that people start doing it. Kind of like the front snap kick. Barely anyone was doing it. Then Anderson does it, and everyone starts using it and even KO'ing guys. Anaconda's too. Nog used it in Pride and suddenly guys started using it.
Ben Saunders has been able to prove that it works, but he didn't pull it off against a top 5 guy. So until a big name uses it to succeed, guys are going to use the "tried and true" guards.
I also think there are a bunch of misconceptions about RG. The main one being that you need flexibility or long legs. You need that if you're playing a Ben Saunders game. I'm not using dead orchard any time soon. I don't even really play standard rubber guard either. I play a modified meat hook game that's still rubber guard. It's just a variation. If guys trained it enough, they could find their groove and what works for them. But really, using that leg behind the head to control posture is really powerful.