Firstly, we hate paysites. Are you a paysite owner? Well, we hate you, too.
We do it because it will piss you off. Yes, we are assholes. Tough.
Besides, you're only charging for bandwidth, right?
Isn't it so nice of us to contribute our $100/yr to alleviate your bandwidth load?
No? It pisses you off? Great! And now you know why we do this.