Yeah fucking horses is illegal and there is lots of that stuff floating around and I rather see a tentacle that some dudes dick and balls. Heck I rather see a proper Futa than a dude.True. But it's also very realistic that those $250.000 (I question the validity of that though) came mainly from Japanese people.
In the west, non-tentacular sex is legal, and it's easier to identify with a penis than a tentacle, which is why I bet that this fetish is very small, and not quarter-of-a-million sized in the West.
Of course it's there. There are lots of people in here who play games featuring people under 18 too (which is illegal in the west)