Another reason related to 2 is simple convenience. Compared to someones house a bar likely has:
readier access to beverages and food that may be required while socialising.
A large enough area to sit the relevant number of people comortably.
And be in a mutually beneficial location. E.g. if my friends and I all live 10+ miles from the city centre in differing directions it would be very difficult for us all to congregate at ones house, but easier for us to all reach a centre point. Even more so if we are all in the same place for another reason (after work drinks).
The other day, someone did something I didn't expect. It was something many people have done before; something that I thought of as very normal, but that I in no way understood and had not predicted.
As I said, this had happened many time before, so I wrote it off as "me not understanding people" or "people are weird" for a second, like I usually do, before realizing that "bad at" really means "lacking basic knowledge", which I had never realized before.
And then I thought "I should ask someone who is different from me why people do that, and eventually someone will have an answer."
But many people will have many more questions like this. So, what have you observed people doing time and time again, but never understood? Or something that you only understood after a long time or asking someone about it?
And can Less Wrong tell us, not necessarily why (I for one can make up evolutionary psychology fairy tales all day if I want) but what conscious thought process occurs behind these events?