I've heard the SGB2 was primarily released to support the Game Boy Camera/Printer (because supposedly Sega/Atlus' Print Club instant-photo machines were that popular at the time). Would explain why it wasn't released here (and Nintendo went on to make an N64 photo-editing app in Japan called Mario's Photopie).
But I wonder why Nintendo strangely made the SGB2 cart to fit both the SFC and NA SNES (not that I'm against it ).