“bp everyone does”
Thats highly debatable. Nevertheless, I dont want this to digress to a discussion on the Eruv.
It is entirely possible that the reason is because the homes on the blocks mentioned by the OP are rather large and spacious inside with room for the various family members to do their own thing and have their own space. the homes in BP are not all that spacious and especially in warmer weather the last place you want to be is inside on top of everyone else.