Too much of the "bang for your buck" syndrome, from what I've seen, people pay a monthly fee and then have to play it obsessively in order to feel like they've gotten their month's worth of play.

I suppose the only thing RO EVER did right was to have the ability to pay for just a few hours of gameplay, so you could just pay for what you played, rather than pay and then feel like you HAVE to play it or you've wasted your money.