Likely because this game is so obscure. The NES Megaman games get all the fame, and rightly so, they're great. But the GameBoy games were all quite good. Even Biox's Megaman 2 GB once you give it a totally new sound engine lol
Perhaps this is a lot to ask, but is there any way you could create a tutorial on how to compile these romhacks using the music? I'm more than willing to purchase RushJet's work, I just really want to use them in game and you don't seem willing to distribute the hack you're using.