Theres often more interesting stuff to be said about why something failed than about a language that is mainstream designed by committee and compromise.

I don't think it's fair to say UML itself failed. We did get to a point where to see a project modeled in UML gives you a strong desire to turn and run (and this is usually the correct thing to do), but it's more to do with abuse and stupid users who don't even make the difference between modeling the behavior and modeling the implementation.