Ongoing friendship and collaboration is important
Ongoing friendship and collaboration is to be contrasted with one-off replies you might get from people if you post something on the internet, or if you ask someone to take a look at something and they add comments to your google doc or something.
The reason I care about ongoing friendship/collaboration is that if I have to contact a new person for every new topic, that creates too much friction/transaction costs which really drains me. Also big projects take a long time to complete, and even giving good feedback takes a long time to really understand what's going on. You can't just have random people on the internet spend 30 minutes and give a great reply (unless they've independently been thinking about this stuff for a long time).
Ongoing friendships are also much more reliable than online question-answering services.
I think one of the reasons that AI safety is not a community is that it's difficult to find these deep connections.
You can also get much deeper conversations going if the other person already basically understands your personality and understands your assumptions/mindset.