With the exception of Blue (and Green), I have at least one copy of every main Pokemon game. I love having all the versions in a series. It helps if I wanna do a challenge, as I can just transfer my Pokemon to a file I don't plan on resetting. I suppose with Pokebank being a thing it's no longer necessary for me to have more than one per series, but eh, I like the series enough to purchase all of the main games.