I remember when MMOs used to be so time consuming (Not just filler content) that playing more than one was akin to comiting social suicide.

Nowdays MMOs are designed for a mass market, everything can be done quickly and easily. The achiles heel of this market space though is casual MMO players are as quick to leave as they are to join. WoW is currently suffering massive player lose due to multiple other MMO's peeling players away due to the lack of "Lasting appeal" WoW content offers.

It's really the battle between having a smaller more loyal playerbase versus expanding your market at the cost of player retention. Both are required for a MMO to thrive, but many companies get lost in the shuffle of trying to cater to both crowds and it rarely works for long.