As a person who has talked about weather with neighbors... It's not necessarily about being uncomfortable. All small talk has a subtext, and in this case I think it's something like:
"Hi neighbor, it's nice to see a familiar face. I'm glad to see that you are alive and well, as am I. I am still a normal non-creepy person who lives near you & who cares that you are doing well. If you ever find yourself in a jam eg. locked out, I'll try to help you, and hope I can rely on you to do the same for me. But I don't necessarily want to be your friend, and I realize that you have other things going on at the moment, so I won't bother or distract you with a conversation that takes longer than an elevator trip or requires emotional vulnerability or introspection."
I think we don't say these things in these words because it takes too long, and it requires engaging with someone on a more personal/honest/vulnerable level than they may really be comfortable with given that I'm basically a total stranger.
