Why would a barista (/waitress/waiter/any other serving staff) be interested in you? They serve hundreds of people a day and are most interested in taking your order as fast as possible. They have other people to serve, taking up not only the time of the barista but also the time of those other people is just rude.
The best way to treat someone as a human is acknowledging their task and being polite.
Funny thing is I've observed more Americans being downright rude to people than others, but that's probably the people I've met more than a general thing.
Of course it's completely different if you interact with people for more than 5 minutes.