I was driving down the M1 the other day waving like crazy at all the other drivers out on the road. Not one waved back. Can you believe it? What's up with these people?
I suspect that the reason is that the drivers aren't driving along the M1 for enjoyment, they are driving down the M1 purely to get somewhere. Cyclists, on the other hand, tend to cycle because they gain some pleasure from cycling. Thus the waving thing is merely about acknowledging others with a common interest. Similarly, people don't acknowledge strangers when walking down the pavement but if they are walking for pleasure (e.g. rambling/hiking) then it is common to exchange a "good morning" or similar when passing others doing similar.