A lot of people in this thread have touched on great points, so nothing to add at a general level but will add some anecdotal observations.
I'm generally very happy and my "default" mood is to be happy and optimistic about things. It helps that I've managed to make (and keep) a very small, but very close and loyal group of friends, and I'm also close with my family, so all of that is awesome. But beyond that, I have still grown colder as a person as I've aged, partially because of the things I list below. Anyway, I've noticed that:
(1) Some people I get to know complain that it's difficult making friends, yet they themselves don't put in that much effort at making friends.
(2) Somewhat related to #1, quite often people try to come across as being "oh my god so busy". But when you look at the situation closer, you can't help but think, "what the fuck are you so BUSY with? You don't have kids, you don't have a back-breaking job, you don't even have many hobbies." So people are busy with... Looking at their phones, I guess?
(3) This is especially true in American suburbs, but there doesn't seem to be any sense of community. You get a lot of nice looking single family homes, but whenever I've seen people, neighbors almost never interact with each other. It's bizarre. So you get a lot of isolation, and parents lose themselves in either booze or other nonsense, and kids bury themselves in video games or TikTok.
(4) In the cities, it's slightly different but ultimately, the same. In the cities, there are TOO MANY people, so any given person may see the rest of the people as dispensable and unnecessary. There's no sense of community; these days the only thing that binds people together is politics (which in the city is overwhelming liberal/progressive; most definitely not my jam). There's so little sense of community, that sometimes people will witness an event of somebody getting beat up or something. No one intervenes to help, but you can be assured that at least 3-4 people are recording the event on their cell phones.
I'm not a religious guy (mostly agnostic on that front) but... love it or hate it, religion HAS, in my anecdotal observational experience, been the one thing to guarantee a sense of community. Everywhere I have ever been, religion is the one thing that makes people to go into the same physical space and (gasp!) talk to each other.
That was a long ramble but that's my two cents for now. Cheers!