SOE got lucky making the first well known one, Everquest, and they haven't been able to duplicate the success yet.
Not even that, MindTrigger: SOE didn't make EverQuest, they bought it--lock, stock and barrel. It was designed and developed by Verant, the key personnel of which now form the core of Sigil, the developers of Vangaurd: Saga of Heroes. Sony recently realized the massive scope of their rapidly-compounding errors and scrambled to buy the publishing rights for Vanguard, thus reacquiring the only real MMOG talent that ever worked for them. The circle of inanity is complete, but at least they finally realized their error.
Maybe they'll listen to McQuaid & Company a little more closely this time. Maybe.