Personally, I think that unless Howard and Hot Toys only makes what they like, they're not making X-Men figures because of profitability. They're a business. If they thought they could make anywhere near as much per X-Men figure as Batman or Iron Man, we'd have a dozen or two on our shelves. Between the 5 X-Men movies, there are at least 20 great looking characters they could have make figures of.
Whether their research told them they won't sell, or the gauge was the sale of Wolverine origins and later X3 Wolverine, they must not see the money there.
My only other theory, is that it has something to do with the studio. Maybe Sony is not as cooperative as Marvel Studios? Sony does hold the Spiderman and X license??????
Its sucks they don't make more from those 2 licenses. But the reality is, HT equals Batman, Iron Man and Predator ( sorry if I'm missing any others ). And they occassionaly sprinkle in all the other stuff. I doubt that will ever change.