They can prevent some things though. Aldo's motorcycle accident comes to mind in recent events.
Drop in the ocean though, 99% of injuries are from the actual fight training.
I don't see why they can't regulate training a bit ... I know these guys think they need to be as close to the real thing in training to be ready for it, but if half the time you're getting seriously injured then it's pointless. Just force training with more padding etc. and leave the 100% fighting for fight night.