Because most cultures don’t demand that men remain virgins until marriage like they do for women.
We supposed to crose deals.
Islam, Christianity, and Judaism do.
Christianity and Islam being the two main world religions, I’d say most cultures do have that ideal.
I don’t know about Buddhist or Hindu requirements.
I should probably take out Islam, at least more recently, because I have read that they are having temporary virginity fatwas or some such nonsense.
Also, to be more clear, premarital sex is forbidden. If you are not a virgin due to being raped, or being widowed, or some other reason other than fornication, virginity is not required.