For men, the fetish appeals to those who enjoy seeing women humiliated and subjugated by something that isn't even human. For women, the fetish appeals to those who've secretly always wanted to have sex with Squiddly Diddly.
While Maeda may have created the modern tentacle rape, he wasn't the inventor--not even close. Maeda was preceded by Katsushika Hokusai, an artist from the late 18th and early 19th century. Hokusai was the artist of the "Thirty-Six Views of Mount Fuji," an internationally recognized series of prints that earned him fame both locally and globally. Also: he liked him some tentacles.
Hokusai's "The Dream Of The Fisherman's Wife" is speculated to be the first instance of tentacle erotica, so by all means don't click that link if you're at work, there are children present or you have a soul.
But before you go calling Japan a nation of psychotic fish diddlers, check out "Tentacles of Desire: The Man Who Loved Cephalopods." Contained within is the story of Joshua Handley, an English artist in the late 19th century whose travels to Japan resulted in an obsession with tentacle erotica.