He was probably infertile.
The Jews, with their active attention to circumcision, knew a thing or two. They classified people into six genders:
1. Male
2. Female
3. Androgyne (both parts)
4. Tumtum (not really clearly defined)
5. Aylonit (Basically a barren female and/or someone who develops male secondary characteristics at puberty)
6. Saris (A barren male which may have some breast growth)
More Than Just Male and Female: The Six Genders in Classical Judaism — SOJOURN
The Saris appeared to have most of the rights of a typical male, with the exception of not being able to serve in the Sanhedrin, but generally in Judaism the purpose of marriage was not for "love" but reproduction. People who didn't seem likely to be able to do the deed were probably left out of the equation.
Now, why would he have been a Saris? Well, his mother effectively had no human male genetic material, and effectively was given a child through the same miracle as many animal species, parthenogenesis. Well, what do we know of parthenogenesis. It basically produces a clone of the mother. So if Jesus was essentially his mother's son, so to speak, identical in all aspects but the appearance of manhood, it stands to reason that his equipment probably didn't work.