I could easily see a 30% decline in userbase due to silly restrictions such as this. Sure, you could just start a new account using an email address, but then you've lost all your previous games, and all your friends will have to re-associate you with the new username. It's frankly easier to just say "uh, they want what? no..." and close the app, being reminded of the experience anytime you think of playing again until you remove it from your phone.