There are several reasons why. You can browse the old posts to learn some of the details. Essentially, there has never been enough interest in MM9 to support a more extensive repair or modding effort. Support from UbiSoft and LithTech is non-existent.
An essential requirement would be modifying the Lithtech2 engine to work on modern operating systems. I've been in contact with someone who is trying to do just that. That would make a mod for MM9 possible, so perhaps we'll be able to do something in the future. Don't count on it, though.