" The answer is, that I don’t know exactly, but we can explore some ideas about what might be wrong and what a helping process might look like.
I know this because I used to be one of these people.
The big lie that a nerd tells him or herself is that they will make a satisfying life for themselves based purely on their intellectual pursuits.
They are good for mutually reinforcing the idea of how great it is to work on the chosen field, but they aren’t good for intimacy.
Too bad because intimacy is, for most people, ultimately what gives meaning to life.
They are so very competent at what they do intellectually that they cannot stand the thought of having to go back to being an absolute beginner and trying to figure out how to be with other people.
The whole idea of being an adult who is a virgin (or a relationship virgin anyway even if not a physical one) is deeply shameful and embarrassing and people tend to avoid dealing with what is deeply shameful and embarrassing.
These are not balanced people with rich social lives.
Instead, these are people who spend holidays writing papers.
Computer science is a big one for many nerds (or that subspecies of nerd who proudly call themselves "geek"), but any non-social intellectual pursuit will do.
Chemistry fits the profile as would most any academic pursuit.
His main concern is that he will not succeed in finding a life-partner and will not raise a family (which he dearly wishes to do).