I have a friend like this, except he makes 100K a year, drives a BMW, and spends all his money on clothes and guns. He tries with women but doesn't really get very far. A few personality issues, can be kind of a dick sometimes, but basically a decent person. But other than that, there's no real excuse. He'd never go with a hooker or anything like that, has really high standards, wants to get married, but his parental situation was nuts so he's got no help there. I guess in instances like that you really can only count on your friends. OP, give him a break, have a little sympathy for the lost, and try to help him out of the dark. Also he needs to come back to earth too, he's been out there in toyland, being master of his domain. Don't give up on your fellow man, but just realize the longer you leave it, the worse it gets.
And I should probably eventually maybe start being a better friend too.
Re: how it happens? I guess they wait around for love stories or something to happen. Most people don't realize how much of socializing is really kind of predatory. Sure it's all wide eyes and smiles, but nerves are there for a reason and some people never get past the nerves. Some people don't hunt well, don't like putting themselves at risk, don't meet people well, don't know how to size up people for receptiveness, don't like rejection etc. It happens, and unless they meet someone by chance or a woman is forward herself, or you never put yourself in the situation for those things to happen, you just might be a 30 yr old virgin.