I wonder how much of the changed behavior comes from the less intrusive communication options having gotten much lower effort. Even calling someone unannounced is almost unthinkable except if it's an emergency. I think that's because it's so easy to just send a text message first to ask if it's convenient. In the past text messages weren't as common. Before that, I could have called for example before stopping by a friend's house. However, I would have had to call the landline which nobody might have answered because maybe they were outside. It would also have been disruptive because anyone in their household would have felt like they needed to answer. So why not just stop by if I am passing by anyways? Now though, I better first send a text, then it's not ideal right now because they are cooking or something, so we postpone, even though I could have just helped with the cooking. But nobody wants to propose cooking together. It feels like you are imposing from both sides, but probably both sides would enjoy it. We are just overthinking it.
Anecdotal data for another factor: Too much effort is made! I've recently tried to make an effort to build up more of a friend network and turn some acquaintances into friends. I've noticed that we try to make everything so "nice" that it becomes inconvenient. The hosts always spend at least an hour getting their place ready and prepping food. This leads to a "barrier entry" for getting together that makes these events less. I even brought that up one time, but hosts seem unable to reduce the effort they make. Guests commonly bring gifts. Nobody needs the gifts or the super tidy home to visit. Just ring the doorbell, grab a beer and let's just hang! I say that, but I'd never do this either because it would feel like a transgression. The only exception I've noticed is that sometimes we'll end up chatting with neighbors for a prolonged time when we randomly run into each other while going for a walk or something. However, nobody would ever say "let's take this party inside". It seems to have become cultural and I am not sure how to fix this as an individual. I think part of it is that we are always busy now or feel like we should be. Gotta run those errands, work on my side project, etc.