American here. I think many of us are kind of socially unmoored, and actually don't know how to take a neutral tone, and get anxious when someone takes a neutral tone with us. Almost like we're so insecure that we need constant positive feedback/reassurance that we're in a friendly situation. I've been around this my whole life and haven't gotten used to it, but I do the overly friendly act when it seems that people are expecting it. It doesn't cost me anything, and it seems to help people leave an interaction feeling secure.