I'm 2 months late, but I think the prevalence of this shut-in attitude on chans are just a symptom of the society we live in.
Since the 50s-60s, the cost of everything relative to salaries has increased (housing, food, transports, etc.) except electronics.
We live in highly competitive societies where getting almost any kind of job now require having a specialized degree.
City centers became basically shopping malls where nothing happens for free. Big cities, where all the fun niche stuff in art, science and entertainment for weirdos happen, are continuously getting more and more gentrified and becoming less and less affordable.
You won't find any alcoholic Situationnists fooling around in the streets of Paris with walkie-talkies anymore, but only over-stressed workers who has no time to do anything after their 2 hours long commutes, tourists exploring the parts of the city landscaped for tourism, and members of the European upper(-middle) class being busy doing God knows what. And I'm pretty sure it is the same in London, New York, etc.
What I wanted to convey by saying all of this is that I guess introverted people nowadays don't really want to engage in what is happening outside when school/work is over. They prefer to retreat with their cheap computers and this very interesting and bigger-than-life Internet thing, where art, science and entertainment is cheap as fuarrrk, and you can interact with people who have the same interests as you.
We all became atomized because life is so dull outside of the internet and its infinite varieties of vidya, movies, music, etc, if you aren't interested in going bars with overpriced drinks, soykafty music and annoying bouncers. Anything that isn't part of the vapid late-stage capitalist mass culture is hard to get by in the outside world.
Also, to expand on competitiveness, I want to add that the mainstream conception of dating is a horrible game where you have play by a ton of unwritten rules and are expected to do this and pay for this and so on, the goal is to act like the character of a Hollywood romantic-comedy, and is kinda akin to having a job interview. No wonder there are so many virgins on chans. The best way to meet a partner outside of that terrible formalized approach is to go outside and meet people who share your interests. But as I said, the outside is pretty dull compared to the internet : there are no more arcades, cinemas are expensive, vibrant alternative music scenes are only present in big cities, etc. it's predicted that millenials will have less partners in their life than their parents and grand-parents.
Anyway, it feels good to rant about that.