Because we're guys and have dicks obviously? Not really sure why else someone would like perverted anime. It's like asking why guys like porno or hentai.
For me its because I wish I was in their situations.
I wish some random hot-ass chick would crash into me and we would end up on the ground in a perverted position. Or I end up living together with a hot-ass chick and walk in on her while she's getting undressed in the shower. Or the occasional extremely forward approach given to you by a hot-ass chick is welcome as well. Also these girls do cute things and become easily embarrassed which leads them to overreact which in turn makes them even more cuter.
because dat's how human brain works for prevent extinction, every human being(especially man) need "arousal" to preserve humankind, I bet all men will *Stand up* if you see a perverted animation [unless you're Impotent].
and about why some people loves it when others like it? it all because the differences in tastes, it similiar with all discussion about 'Loli', or 'Furries',or 'rape'.
but the primary in general for me, I think "when it comes to men, it comes to his libido" it just how our brain function.......
the most simple reason I think is "because it was fapable"
h-manga and hentai tend to make me laugh more than they do arouse me.
Not that I've never been aroused by hentai before, but it is usually not the case as it is too funny watching the girls with breasts larger than my head act all shy after they had just stripped willingly for a guy they've know for a day or two.
As strange as it may seem, I'm not a fan of ecchii anime, full of fan service--in fact, I despise it. I find it to be a cheap way to get the audience's attention; it just seems like they don't have enough "confidence" in it's originality so they need to throw in some excessive jiggling, or have a guy trip, and conveniently pull on some girl's (who just, [un]fortunately, happens to be in his hands direction) shirt collar, or even fall into her breasts. I don't look at people differently for liking these things--who am I to judge?--but they just aren't for me, and it kind of disappoints me to see such things. (ie. Queen's Blade, or HotD)
Like others, I don't really watch anime for the perversion; there's hentai for that. I like a good plot, good animation, good setting, good characters/development, and good voice acting. The fanservice is just a bonus that's been overused and abused.
Well I like ecchi if it has a good story. I couldn't continue Green Green or Queen's Blade because I couldn't take them seriously. Hentai it doesn't matter because I want to watch it because of the thrill not the story. Trust me the stories in hentai and how they end up in certain sexual situations are just plain preposterous.
guys like perverted anime because, as an illustrated medium, anime is detached from reality, so we can experience the pleasures of perversion without condoning what, if it was to take place in reality, would be morally horrific.