People do want something different, the problem is that the only "different" things we get are from small indie developers that don't have nearly the budget or marketing to compete with AAA games and thus only a small audience knows of them.
When was the last time you heard of a AAA backed sandbox mmo? Since UO the only big sandbox mmo's have been indie developed.
The problem with WoW is that it's not an example of the "normal" mmo in terms of subscribers/success. MMO's before WoW generally had a much much smaller average subscriber base, and they were considered "successes" but these days people only think of WoW as being successful and if they can't reach that goal they aren't.
Unfortunately people are generally stupid. A lot of players think they know what they want, when in fact they have no idea what they want. I bet a lot of people will scoff at the idea of what games like EQNext and Camelot Unchained are proposing, but if they deliver you will see them flocking to it saying they wanted something like that all along. At the same time, many players will say OMG I can't wait for a game like this, and then play it for 30 days and say NM I really just wanted WoW 2.0 because they have issues coping with anything remotely different from what they used to.