When driving a car do you wave at other car drivers and expect them to wave back? When walking do you expect other pedestrians to wave back at you? When boarding the bus do you expect everyone inside to wave at you? When riding the airplane do you expect everyone to wave back at you? The real question is why you feel you require this special attention/validation from complete strangers? Do you lack self-esteem?

I don't consider riding my bike to be a social experience. I'm concentrated on the task of riding, and my safety. I'd expect that's pretty normal, but people are weird so I could be wrong.