We may be thinking too much here...
I've been riding as an adult for almost 40 years. When I started, in the early '70s, I might go a week or more without seeing another cyclist. I moved from the San Francisco area to Reno, Nev., in 1978, and rode for more than a year here before I saw ANY adult riders. In those days, we all waved.
When I do the same weekend rides now that I did in, say, 1980, I can easily see from a dozen to as many as 50 riders. I kept track last Saturday, the first nice day in several weeks, and I encountered 37 riders on an 18-mile loop. That's a wave every half-mile, on average.
FWIW, I date back to the days when imported cars were rare and drivers used to wave to each other. There was a strict protocol--MG and Triumph owners could wave to each other, but a Jaguar owner wasn't required to acknowledge a wave from a Sunbeam, and so on and on and on.
That all vanished sometime in the early '70s, and it's just as well. Nothing personal, but I'm waved out.