It might have to do with the PSP games actually.
Remember how Capcom promised a bunch of stuff for the Megaman X Collection, yet most of those things didn't make the cut?
It's because the Megaman creator (forgot his name) didn't want to take away from the PSP remakes and told Capcom to remove all the new stuff in the compilations. If I remember correctly, the X1 arranged soundtrack was taken out because it's being used in Maverick Hunter X for example.
The same thing might've happened to the GBA game and maybe they pulled the plug on it altogether.
It sucks really.
Link.