I'm not sure if you have checked out WoW lately, but it's actually a pretty beautiful game. I think generally they want the tech specs to be a low barrier to entry for a game where they want millions of players playing concurrently. It also cannot be super heavy or things like raids and battlegrounds would chug.
One thing that Blizzard has always been good about it making games that can run on a potato. It'll look like crap and your view distance will be obnoxiously short, but you can run WoW on a potato of a laptop and still participate in the core gameplay. Obviously, there's lots of options to crank up the graphics to 11/10 if you have a powerful computer, but I really appreciate that they lower the hardware barrier to entry where they can.
EvE Online used to win Best Graphics of the year frequently. I dunno if they still do. They're also the only MMO that I know of to use in game footage for their trailers. It would be nice if the gameplay was decent.