I don't think the extent to which people feel comfortable socialising stays constant. I'm naturally introverted, and with a few exceptions I find being in other people's company exhausting - however I'm not a complete loner, and do enjoy it in smallish doses. It's as if I have a "level of fitness" socially. In my head, I consider that "forcing" myself to go to social events maintains this fitness.

Now think of the pandemic lockdown. It could have caused introverts to have lost their social fitness entirely.