Perhaps because the original game sucked? We are CV fans and we like it, but go around there, few people outof us liked the Adventure - remember, it was made faster than normal because it was almost launched with the Game boy, and the team was too unexperienced - so, why make exactly the original? why not only take the best - enemies, conception of stages - and make it better? This is what remakes should be - even if this is a reimagining - the best of the originals and improved.
And there is music from Belmont's revenge. Yes, I know, but it's something. Adventure original music was not that good.