It doesn't require people to not want to socialise for it to have that effect. It merely requires a proportion of visits to be unwanted or inconvenient then and there.
> You might be annoyed by unexpected visitors, but to others it may be a delightful surprise.
It might be to some. Even to me sometimes. But it was enough of a nuisance that the unwanted visit - as I've pointed out already - became a significant a trope in fiction, and a part of our cultural fabric. The "we were in the neighbourhood" was e.g. a regular vehicle for visits in TV series that has now largely disappeared except when it is used to highlight someone intentionally sidestepping social norms to impose an unwanted visit.
You dismissed fiction earlier, for no good reason: A widespread trope doesn't arise in a vacuum. It worked as a trope in fiction because it was a real and significant thing.
You've had this explained to you at length now. I struggle to see why you find it hard to understand, so I'm leaning towards thinking you're being intentionally obtuse about it at this point.
I agree that mobile phones have a role in the reduction of socializing.
However, I don't agree with the reason you've given, and I have at least two objections:
1. Mobile phones don't actually shut down unplanned socializing. On the contrary, they make it easier to have unplanned socializing, because they allow you to contact another person no matter when or where either of you happen to be.
2. There's no empirical evidence that a significant number of unexpected visits in the past were unwanted. Surely some were, but not nearly enough IMO to explain the dramatic reduction of in-person socializing.
My theory, in contrast, is that the ubiqiutious internet access of smartphones has addicted people to the practically limitless forms of entertainment and attention-grabbing online, and this internet browsing has usurped in-person socializing as a pastime. This change has nothing to do with how easy or hard it is to arrange visits. People have stopped dropping by because they don't want to drop by, not because they can't conveniently drop by.
For the same reason, people have also cut down on non-social activities like reading books. They aren't replacing socializing with book reading.
> You dismissed fiction earlier, for no good reason: A widespread trope doesn't arise in a vacuum.
I dismissed fiction because it deliberately exaggerates for effect, e.g., comedic effect. There may be a grain of truth to it, but fiction by definition is not an accurate reflection of reality.
> I struggle to see why you find it hard to understand,
I'm not struggling to understand. I simply disagree with your analysis.
> so I'm leaning towards thinking you're being intentionally obtuse about it at this point.
You can lean whatever way you want, but you're wrong, and you're also wrong about me "forgetting" the rest of the world when the submitted article is explicitly about the United States: https://news.ycombinator.com/item?id=49894515