A lot of friendships aren't that deep. I've had work colleagues I really liked and even socialized with outside the workplace, and yet, if they left the company or retired... faded away. If it takes real effort to keep up contact, you get a lot more choosy.

COVID also hit pretty bad. Speaking from personal experience, several friends that we saw once or twice a year at informally recurring BBQ/brunch/etc. kind of occasions have faded away as that series was interrupted and never restarted.

And finally... you learn who you are as you age. Friends who seemed cool, who seemed to have the answers... may not be so great from a mature perspective.

Feel the same way about COVID. It damaged the social fabric in ways that have not recovered. I think a lot of people realized that maybe they never really liked socializing as much as they thought they did. I also think it just kind of reset people's expectations around socializing. The other big one to me, that it also unleashed, was inflation. Dining out, sporting events, concerts etc are all way more expensive than they used to be. Places are still busy and games are still packed but the prices are way higher, more evidence of the K shaped economy where only the top stratas are spending. Also, and this is subjective, it feels a bit more performative, as in people are going because it signals they have the means (edit: and the general instagram-ification of our culture.)

How deep do they have to be?

I just don't want to be "that guy who was right... and alone"

In any case, if you need other people, doing the work will pay off. you need it.

If you got phone number or online communication , it should not be that hard to keep up