There are always multiple factors. As a guy who doesn't overly want sex, some of it comes down to choice. Obviously I would want to partake in sex with the right person. The problem is that for some people more than others, finding the right person can be extremely challenging and something that demands effort and tests character. For those who think like that, it's really easy to give up, which would keep them a virgin. There is also some element of randomness on when that person 'pops up', if they do.