> These two are generally adhered to in the US as well

I'm not sure; granted I did not visit a lot of places in the US, but when I was there (Miami/Denver/Phoenix), I virtually never saw e.g. a customer greets the cashier when buying things.

That would have been considered extremely rude in the past. But beginning with millennials, these kinds of "mandatory" niceties began to fall away. Now with smartphones, hardly anyone looks up at each anymore. Why would they? We all know how the transaction is gonna go.