If they made a Pokémon Snap sequel, I would buy the new console just to play it. XD Seriously, it's one of the best Pokémon games ever. Getting all 400+ Pokémon would be crazy, but they don't have to put them all in the game.
I don't think there's a particular reason, but I really liked the fact Johto looked "japaneezy" (I think I know the song pkmn_GSC is referring to XD), because Japan fascinates me and it was somewhat like traveling in it. :)