I have definitely been socially isolated my entire life to some degree or another. But much more so in adulthood. Again, I suggest that this is relatively common, not something that happens to only a few million people.
One aspect that is being glossed over is the amount of socialization or let's call it "pseudo-social" activity that is happening over the internet for these people.
I'm someone who generally does not have friends, leaves the apartment literally only a handful of times per month to take the garbage out and maybe buy groceries once or twice a month if I am trying to save money versus Instacart.
For me it comes down to money. I have a health issue that makes me fatigued etc. and don't have money for health insurance. I don't have money to go to restaurants or otherwise waste going out. So I stay home.
Because I'm always in a poor health and financial state, I feel uncomfortable trying to do any "real" socialization.
But I have always been trying one way or another to get to a point where I have a "real" online business that allows me to actually thrive. Such as buying a car and a house, getting health insurance and addressing my health issues, or paying taxes.
But what I have managed so far is usually just enough to scrape by. There have been some minor successes here and there but rarely have I ever felt like I had enough to truly meet my basic needs such as the health concerns or financial stability.
Anyway, I think it's easy to get in a position with health and financial challenges, maybe just a series of low-paying contracts, where some degree of social isolation is just practical and realistic.