In American culture, hyper-individualism has become a virtue somehow but this too is just a symptom of capitalism. Why? Because people who act collectively are a threat to capitalist power structures.
The whole "gig economy" is nothing more than needing a 2nd and 3rd job just to survive as real wages continue to stagnate or decline and costs keeping going up. That's less free time.
The Internet is a negative here too. Physical proximity has historically had huge power in creating freindships. But capitalism rears its ugly head here too in the destruction of so-called "third places".
High housing prices hurt everybody. It destroys community spaces. Hobbies that were once cheap escapes become way too expensive. Housing costs are an input into everything. Take spiraling childcare costs. You need physical space. That's now way more expensive.
Lastly, there is a natural trend for people who marry and have children to replace friends with family. There is an issue of shared life experiences. 50+ years ago pretty much everyone is in the same boat. Now? By choice or necessity, people are opting out of this "traditional" life and this naturally creates a divide.