When my husband was a teenager his Mom was very worried that he would never have a girlfriend as he stayed at home and played Star Craft all the time. A friend of hers tried to calm her saying that “a true girlfriend” would find him at home and there was no need to go out. So, guess where we met?! Yes, that’s right, we met at his place at a party thrown by his roommate.
This is curious, if I'm not mistaken and if I understood you correctly, someone is supposed to develop an introverted personality because the mother is not available to the child when he is just a child, however, now, in adulthood, when the mother should not worry so much about the son, it is when she worries about the son getting a couple.
Well, generally introversion is a genetically inherited personality trait (research shows that it is connected with certain brain structures). However, environmental factors also play a role in forming one's personality. Thus, a mother's availability could influence a baby personality toward extroversion. In social science, more often there are many factors that influence individuals than a single one. Usually, when there is a genetic predisposition to something, environmental factors could strengthen it or restrict it. So in this case, if someone has a predisposition to be an introvert, what happens later during their upbringing (environmental factors) could strengthen their introversion or restrict it.
The example I gave with my husband's mother is only to show the fun fact that we actually met at his home as her friend suggested a decade earlier :)
I see, so there is a predominant biological factor too, quite interesting. A very particular anecdote that you have told us, thanks for sharing it with us.