I think it's mostly the current batch of writers not really giving a hoot about them one way or another.
One could even make a case for their momentum being purposefully killed off for whatever reason, but it's all moot now. Unlike the comic books, we don't have time machines and things are what they are currently. The few that managed to gain legs have moved onto other things and the rest are now forever doomed to be interchangeable background extra's.
I don't have to like it, but I do not foresee it changing either.