psychological subjection, if theymos makes a pizza, many will be tempted to vote for theymos' pizza even if it's not the most beautiful pizza
to have voters who vote objectively, in my opinion, we need to publish the pizzas anonymously so people can really vote for the one they like
Publishing the pizzas anonymously would require more effort in coming up with the best way to do it, and in my opinion it is going to reduce the fun in the contest. While i don't think Theymos would participate, but if he does, and he gets the most votes, then he will be one of the winners, there is no need to complicate things.