The big problem, other than getting funding, is that Babylon 5 was always extremely serial in nature. It was designed to be a novel for television and that shows. It doesn't do stand-along stories all that well. Killing off Lyta and Lenier wouldn't have been all that powerful if you didn't know who they were, and without five seasons of television to get attached to them.
None of the Babylon 5 TV movies actually works as a stand-alone (except possibly River of Souls, which was pretty mediocre).
Compare to franchies which do have long-running movie series, which tend to be highly episodic so that a new view can jump right in.