Men sometimes like it for the same reason women sometimes like it: it's a sexual act, and sexual acts can be enjoyable. Some variety among the sexual acts a couple engages in can keep things especially enjoyable.
On a personal note, Mrs. Shackleford is quite prone to UTIs. Because of that, sex for us means preventative preparations. If sex is planned, she'll make it a point to drink more & take some cranberry supplements in the hours before. She always cleans up first, and I often do, too.
Well, sometimes we're just snuggled up first thing in the morning or at the end of a tiring day and don't want to stop and take the time to do all that, but we still crave the intimacy of penetration. In those moments, anal becomes an alternative. It's usually no more than just working the head in, but it's still me inside her.
Like most activities, if she wants to do it and to what extent varies, but generally speaking, as long as I control myself and I'm not just ramming it in like a psychopath, she enjoys it. There was one time a while back when we got a bit spontaneous in the kitchen one afternoon, and after I started playing a bit back there, she just bluntly told me, "Put it in."
Ultimately, people like what they like sexually simply because it's enjoyable to them. It just is. As long as their partner(s) enjoy the same thing or at least are willing to play along, just accept it. Threads like this are like going on a food website and asking, "Why do some of you like apple pie?"