Because MMOs can be way too fun ;) Lets face it - if you've played a good MMO, chances are some of your moments playing them are among the best gaming times you've had!

Keyword phrase there is "a good MMO." Bad MMOs are just, well... bad.

They do mimic the physical drug addiction thing, that early good hit, you just keep chasing it but it will (very probably) just never be duplicated. (not saying I know this from experience, just this is what's said) I know my early best experience with a old hard game, big death penalty, (original Everquest Kunark era) I've not had such a height of fun with anything since. Some fun here/there yes, but just not that length of time and level of fun.