America used to be awash with grassroots social institutions. I know an elderly gent who belonged to the Lions _and_ two similar organizations. When my mother was young, there were dances and dinners multiple nights a week. Which, for me, raises the question why weren't these things passed down? Why weren't the young a kind of apprentices to the old? That seems like the natural progression. But we see this generational rift in many areas of American life, including on the job training or something as practical as home cooking. It's like gazing into the past across a cataclysmic divide.
Staying at home is as entertaining as it’s ever been: video games, Netflix, don’t even get me started on short-form content.
I think a big part is the decline in organized religion.
There used to be a lot of disdain on HN against people who were "just partying". While the geeks stayed home, learned for school or job yadda yadda. People who socialize were always maligned here, their socializing was supposed reason why they earned less money.
And that attitude is one part of the answer. Second is that home entertainment became easier and more fun, so people stay home watching movies, browsing internet, what have you instead of going out. And overtime, dance places became emptier and organizers demotivated.
It was technology. With greater efficiency, came also greater separation and distance at home and with family and community and our initiatory rituals/rites.
We used to use community to pass those down, but now the average American family gets divided from each other at an early age as soon as the distraction and ideology from technology like screens and things social media comes into play.
Edit: Before internet, there were other forms of "social media" at play attempting to extract the attention of the individual units of the family and community, but they weren't as effective. With the internet they are more effective.
It's trite, but I think a part of it is "because the internet happened" - and I don't mean just today's enshittification era but also the "good old times" everyone seems to remember fondly here. At some point, the internet was full of that kind of community spirit that you described, but of course this meant that people were more likely to direct their energy to online community building than to real-life stuff. And unfortunately online communities didn't always teach the skills that offline communities required, and also probably contributed a lot to the "consumer mindset" the OP warns against...