May I just chime in with another little note. I really don't know whether this will help to clarify things any further to the OP, but since I am enjoying a cup of coffee and have some time on my hands....
I believe your original question was why gay men are attracted to a hairy arse and later on you ask why would anyone be interested in engaging in anal sex. Correct me if I am wrong.
I shall not address the point of a hairy arse specifically, since many other posters have addressed the issue of personal taste in that matter. However, with regards to the choice for anal sex let me try to elucidate. I assume that as a heterosexual you enjoy vaginal sex, right? It is pleasureable to rub your penis in and out of a vagina, simple. Perhaps you also enjoy oral sex; it is pleasurable to have your penis rubbed by a tongue plus lips, simple. Now, let's move on to bisexual or homosexual men. Yes, they can enjoy oral sex in the same way you do. Same rubbing/friction equation, right? A penis is a penis - it responds to the same kind of physical stimulation whether you are heterosexual, bisexual or homosexual. Now, AMAZINGLY, there is another orifice we human beings possess. And someone long ago discovered that if you stick your penis in there, you actually get a similar rubbing/friction sensation. Yes, we know it's an exit, yes we know it's for excretion, but we can clean it - we have the technology. So, all else being equal, why NOT use the exit for physical pleasure? Simple. I hope this clarifies why anal sex is not restricted to an individual's sexual persuasion. And who knows, perhaps this helps to answer your original question too.
Live long and proper (with or without anal sex)