Asking this question in this way (demanding an explanation) frames it so that people will instinctively feel defensive. There’s no shame in being a virgin. You aren’t entitled to an explanation from anyone about why.
Because I never had sex.
Too busy watching the 40 Year Old Virgin
There could be lots of reason for not having sex:
Asexual
Low sex drive
Never found a person they could connect with like that
Being an awful person / falling into the internet incel category
Different motivations in life that they didn’t feel the need for sex
Medical problems - this could cover a lot from psychological issues to physical issues
Fear of pregnancy / failure of birth control
Strict religion
Nervous/anxious/shy/awkward personality (like in the film)
It’s a pretty good movie, might watch it again.
It’s been such a long time that I can’t actually remember what happens outside of the waxing scene. Time to watch it again.
Because some people apparently prefer to spend their time reading stupid questions online.
If you’re that old, you probably want to be, and that’s totally okay.