I'm not a parent so don't really understand, but I was never really comfortable with the idea of doggedly perpetuating a lie to your kids.
I mean, sure, when they're very little then it's probably quite exciting to think there's magic in the world, but as soon as they're old enough to go "hey dad, Santa's not real, is he?" then why would you continue to lie about it? Parents are the people they trust the most in the whole world and you're undermining that trust.
When they find out the truth and cry, is it because they're upset about Santa or because they're crushed at the revelation that their parents, the cornerstones of their little world, had been tricking them?
Maybe it'd be different if I had kids, but I just don't get it.