I think this is not America specific and decline could be even steeper when today's kids are gonna grow up.

I see most of the kids are constantly on mobile and when they are not, they feel a void. It was almost similar to not having friends in pre social media age.

I see people getting more and more absorbed in screen so much so to forget greeting people. This happens to me all the time , someone known coming out of elevator, I am ready to greet, but they simply did not notice or noticed too late and vice versa