It's not that easy. Just because it's old doesn't mean it's easy.
Sure, you could put up a Kickstarter for it and get a bunch of money behind the project. But historically, using the premise of building an MMO as a way of raising a bunch of money will result in failing to build that MMO.
A programmer who has experience and talent also has no incentive to recreate UO (think about the modern-day incentive structures for hotshot programmers), unless he was one of the original players. And sadly the overlap between "players of videogames" and "the best game programmers" is actually quite small. Carmack, for example, doesn't play games. Most of the talented gamedevs I know don't actually play them.
Pretty much all of the game devs I know (and I work with quite a few) play games all the time. Both games by others and by themselves (lunchtime playtests).
Because apparently it is still up and running, costs money, and is owned by Electronic Arts? See uo.com - That aside, it seems technologically feasible.
