First of all, China has always had a gender imbalance. The "more men than women" is not a direct result of the One Child Policy, and even historically there has been a gender imbalance in China because of the practice of female infanticide and tendency to not feed daughters during famines.

Secondly, some people prioritize other things over finding a mate. China has a lot of people, and demographically a relatively young population, so they will have a lot of people who are single just because of this.

The lack of freedoms also must have an impact. China has long working hours for many people, which means less time for dating. Some people who live in company provided dorms are actually not allowed to even fraternize with the opposite sex. Hell, even one teaching job I applied to told me during the application process that I'd be in a dorm where I was NOT ALLOWED to bring my girlfriend over.

One last point I'd like to make is that I have a hard time attributing this phenomenon to sex drive because we aren't measuring or counting virgins or the sexually abstinent. We are counting people who are unmarried after a certain age. This doesn't mean they aren't having sex.