Oh, there are a few such companies. Can't think of the names right now, but I did some research into this over the winter. A big problem is that the asset creation is very expensive, and balancing the economic factors is much easier said than done. If you are interested in this, Richard Bartle, inventor of MUD, is the leading thinker in the field.
The best technical system that I know of is the stackless python one developed for Eve Online, which I believe is profitable but has only about $300k players. Mind you, with that number it's insanely complex already. I had to stop playing, because to do so well requires the same level of commitment as a full time job.
I can imagine that asset creation might easily be as large an expense as building the technology.
However, one of the big killers of MMOs is problems with the launch. With some of these large high profile failures, they've already gone through this and worked out at least some of the bugs, so one would assume that this would make them more attractive to buyers.
The best technical system that I know of is the stackless python one developed for Eve Online, which I believe is profitable but has only about $300k players. Mind you, with that number it's insanely complex already. I had to stop playing, because to do so well requires the same level of commitment as a full time job.