Not every dude wants to stick it where the sun don't shine.
Some men call it the final frontier. Whereas the vagina is the entry point of life, the anus is the terminus of the human digestive process. The alpha and the omega. Yet this rear entry (exit, really) holds a mystique and allure that 995 of the 1,001 Arabian nights can't even sniff. Is it the taboo? Is it the fit? Is it a power thing? Whatever the case, you can count me out.
A number of couples save surrendering the female partner's be-hymen* for a special occasion like after they're married or they're bored with sex or out of condoms or drunk. Red-letter days all of them but it seems more like a punishment in my book, for both parties. If I wanted a similar experience, I'd fill a water balloon with two-week old curried lamb slurry, wrap a pink rubber band around the opening and play a recording of someone screaming, "slower, slower, I said slower goddammit. I hate you," in my ear.
Obviously, there are a number of factors in favor of backdoor lovin'.
Some gentlemen (many of them never having spent time in the pokey) prefer the extra-firmness of the rear-facing aperture. Some couples believe the taboo or pain creates an intimacy far more than five centimeters away from conventional love-making. Plus, legends of butt babies be damned, it's not possible to impregnate someone's colon. Some cultures even believe that carnal posterior affection leaves a gal's maidenhood firmly intact. I appreciate a tight squeeze, extra affection, not having to use a barrier method and sexual technicalities of all ilk, however the idea of a trip to the eerie canal turns me off for one very specific reason: poo.
I'm very uncomfortable with poop and that's compounded with proximity to my bare shfonz. There are two great ways to get anything on your genitals and you can entirely eliminate one of them by never jamming them into something. A pair of consenting adults can likely enjoy sodomy without getting anything awful-smelling on themselves but if you play with fire long enough you get burnt (or in this case smeared).
On top of my coprophobia, I have a very specific ideas about what is and what isn't romantic.
First of all, it seems just awful to be on the receiving end. Despite what Sasha Grey films (which I have NEVER seen) imply, I have a hard time wrapping my mind around the idea that a visit to starfish alley is pleasant for the resident. Secondly, I understand that there is much gas involved in the post-coital process. While I understand that women have many of the same gastrointestinal functions as men, I prefer them in the abstract and relatively small doses. James Joyce, I am not. Finally, I want no part in whatever the quid pro quo for a situation like this is.
I'm sure your butt is terribly clean and that other dudes enjoy amateur proctocology for very good reasons. But the rest of us want nothing to do with any sewage treatment plant when there's a perfectly serviceable magical garden just across the way. The only thing I regret, outside of missing another weird human experience on Spaceship Earth, is that my reluctance has made one of my favorite jokes regarding the difference between peanut butter and jam (NSFW) seem hypocritical.
If you decide to give it a try, please use a lubricant that's not going to destroy your condoms, start very slowly and consider taking a decent multivitamin with your breakfast, you're not getting any younger.
*Note: Adam Carolla coined this term, please attribute when using. I came up with the more scatological Cadbury Cherry, which I'd prefer if you just forgot all about.