That possibility had occurred to me. After considering it I shuddered at the lack of humanity such an explanation would imply.

I'm not talking about starting conversations with random strangers. I'm talking about a wave for a wave, a "hello" or even "hi" if two syllables are too much to give a fellow human. You'd use more than that to shoo away a bothersome animal. Even a curt nod or a grunt would be acceptable as a greeting of sorts.

I'm not blowing off the point you made. No doubt you are correct. My point is that it's a pity and a shame that you're right.
I just feel better about the whole thing if I believe stupidity and not utter indifference or cowardice is the reason not to return a simple ritual affirmation of existance. Stupidity I can deal with, I live on the Jersey Shore, where good attitudes come to die.