US culture is pretty different from ours in terms of the way people interact. Kids are encouraged to be precocious and court attention, people make banal and vapid conversation with each other and it is expected. It may on the surface appear they are nicer. People are people, some are nice, some not. Having lived in the US, the way they communicate grates on me and seems insincere rather than nice.
I travel to the US a lot and get the impression they are very friendly. The service staff being nice just for tips is annoying.
Having spoken to people from different countries who have moved to the SFO and LA they have all said same thing, it's really hard to make actual friends, they may appear friendly but it's very superficial. I was surprised to hear this!