It's a family thing.  Parents have been skipping much of the domestic ritual that used to include sit down dinners where one learned manners, some etiquette and how to say please and thank you and mean it.  When you grow up with that, and more of what used to be called polite behavior, it becomes part of your DNA.  What might be called social grace or even social intelligence has, I fear for the most part, gone down the drain.  There are still some hopeful signs but they are too few and far away.