I think nanci is right, they are just aloof. It hurts, though, to feel snubbed. Particularly if you feela kinship to those on two wheels. I always feel friendly towards fellow riders, but I'm not always able to wave or say hello. (I'm huffing and puffing, reading my computer, concentrating on the dog/pedestrian on the trail behind you or spacing out.) And sometimes the hellos can be subtle, such as a raised finger or a nod.

Sarah