Why is not waving at someone you pass on the trail considered snobbish?

Why isn't it just considered 'focused'?

Why should I feel compelled to 'act friendly' to people on a trail who I will never see again after those fleeting seconds in which we pass? To make me feel better? Or to make them feel better?

If I smile and wave at everyone on the trail I pass, my ride will be very happy. But very slooooooow.

K.