Quoted By:
If you're looking for a serious answer, it's multi-faceted. To begin with, Pokemon exploded overseas just in time for 90's kids to experience it through puberty and also the rise of the early internet (and with it, the new age of pornography). Pokemon porn is ingrained in our very upbringing.
Also, for all their flaws Game Freak just has some of the best character designs in the business, especially when it comes to girls. There's just something about aesthetics that they keep nailing, and the characters will keep getting nailed in turn.