To add to what Jack Daniels said:
Another benefit of being able to see the hole cards is that you can get into a player's head so much more and see the mechanics of the hand, because you know what they are holding. When the hole cam is not available, the only time you may be able to learn a little about how they tick is if a hand comes to showdown, or they happen to show their cards. But generally, I would imagine at the final table in the WSOP
, the play is at a level where many pots are won before showdown, resulting in a LOT of mucked hands.