Why do MMORPG communities always suck?

I have played EVERY single popular MMO known to man (both free and pay-to-play) and not one of them had a decent community. I remember playing this one small MMO which had only had a few hundred players and it was alright for a while, but once the game was advertised more, then a lot of shitty people came and ruined it. Why?

FUCKING TRUTH BE TOLD MAPLESTORY IS THE WORST GAME EVER.
I TRY MY BEST TO CONTRIBUTE TO THE HACKING FACTOR THOUGH. ;)