I'll bet this is addressed in the rules of the tournament provider. Sure, you can't wear a mask or even a big hood in a casino for their own security and identity reasons.
But on a televised tournament it's a different consideration. I think that sunglasses are annoying, but it doesn't matter much because they are all stone faced. Not much drama there. If they allowed masks, wouldn't all the players wear one? Or full makeup? That would be funny. I'd pick a Guy Fawkes mask. Maybe Heath Ledger's joker.