Curiously, most of Nintendo’s didn’t; Mario didn’t, Zelda didn’t, Metroid didn’t, Pokémon didn’t, Kirby didn’t.. Nintendo games disappoint confirmed?
Super Mario Bros and The Legend of Zelda got sequels that were completely different games from the originals (and were a lot worse than the originals).
I don't know why Metroid outsold Metroid 2... I hate Metroid in B&W and maybe the Game Boy audience wasn't familiarized with the first game, that might have something to do.
Pokémon Gold & Silver came out for the GBC, that sold much less than the original Game Boy.
I don't really know the Kirby franchise so I won't comment on that.