I agree with this point. When I got my first bike and first started mountain biking, I was so happy to be out on the trails, and enjoyed the perceived comradery with others who I may pass. So I smiled and waved frequently. I never went beyond the point of recreational riding, maybe doing 2 rides per week, but even with that much riding and as the newness fades you realize it's not necessary to smile and wave at everyone. You realize you can do your own thing out there without reciting 15 hellos per ride. You also realize most people don't need or expect your acknolwedgement with every pass. All that is required is common courtesy, not overt friendliness.

I also agree that cyclists tend to focus. It's kinda moving meditation, you get into a rythm, and your mind focuses on guiding your bike over rocky terrain or along stretches of roads. That's one of the healthful benefits of this form of exercise -- you simultaneously vent stress thru physical exertion and thru mind focus. Heck, a friend of mine says its hugely therapeutic to drive his tractor around farmland, because his mind focuses only on keeping that wheel just inside the swath that was cut. To be unnecessarily extroverted would be a distraction, both to yourself and as a matter of common courtesy to others.

Then there is the fact that a bike is a gadget, like a computer. Gadgets and technology like bikes and computers foster geekishness and snobbery. But I don't think it's a malevolent form of snobbery, just an intrinsic fascination and consciousness with the equipment. I think every hobby and niche has its geeks.

There is also an element of competition. Competition need not be an intense desire to be the fastest, best rider out there. But everyone seeks to improve on some level, and even though it may be about self improvement the most readily available reference point is other riders. Even as a solo activity, riders are probably prey to becoming overly competitive, and insecure if left unchecked.

Finally, there is the insecurity of being new to a hobby. One is probably overly self-conscious, and reads too much into the thoughts and expressions of others. Could be nobody is even really noticing or caring about you or your bike at any given moment.