I think that a lot of it is because "social" people seem to be getting more social, loud, extreme, etc. There doesn't seem to be the "middle ground" anymore. I see people like myself who are quiet, introverted, and don't go out much at one end of the scale, and "party" people at the other end who are just too "full on" and exhausting for me to be around.
Back in the 80s you could go to the local pub and just "hang out" with friends, neighbours, colleagues etc - just sitting, having a quiet drink with them, a bit of chit chat, etc., no pressure to "perform" socially, often with background music on low volume from a jukebox etc. You'd meet new people in passing, and your "friend circle" would just naturally expand as you met friends of friends etc.
Nowadays, social events are all so loud, busy, etc., you can't just sit quietly chatting to a few people, it's all excessively loud bands, large crowds of loud people laughing, cheering, getting increasing drunk, etc, you can't hear due to the noise, so it's impossible to have a quiet chat with your friends anymore.
I hadn't really realised it until my son explained why he didn't want to go to pubs, clubs, etc at University. He said exactly as I said above. When he first went to Uni, he went out with his flat mates a couple of times to the Uni bars, common rooms, and a local nightclub - he hated it, as he said it was all the loud, drunken, extraverts who were out and were dominating those places . A few of his flat mates said the same, and they just stopped going out to the Uni bars and clubs. This was someone who'd been happily going to local pubs and clubs etc with his school friends during sixth form with no issues at all. He didn't even want to go to his Uni's "sports bar" to watch football matches etc on the big screens as they were the same - just full of loud people getting drunk - he loves his football but that just wasn't his scene at all.
I do think extraverted people (of which there seem to be more than ever) put off the quieter introverted people from doing social things as they just take over.