Oh **** to waving. Get over it. On busy routes, I don't need to wave to 100+ cyclists. Once you are used to not waving, you don't wave. I certainly don't take offence when walking down the street if you don't say a word when passing, why is it offensive when on a bike? Does Emily Post have a special rule about this?
I've wondered whether it was related primarily to the number of people or cyclists that you encounter.
I know that when I'm riding out on the local rural roads, I hardly see anyone, much less cyclists. As such, if a car comes from the other direction, we're often the only humans in sight, so it's natural to give a quick wave (and this is often standard practice for motorists). Of course, if you are out in these areas, you probably live there, so these folks are probably neighbors or acquaintances, so waving is normal.
When I've gone up to Chicagoland for a group vintage ride, we encounter a lot of other cyclists, so waving constantly would interfere with riding the bike.
Here in Peoria, I don't think I've ever seen enough cyclists in the course of a ride that I wouldn't give a quick wave, but it's pretty low on my list of priorities. I'm much more focused on avoiding cars and potholes when on the road, or watching out for dogs on long leashes when on a MUP.
Steve in Peoria
btw, did anyone else watch Si's video on GCN about comparing his Merckx replica with a low cost modern bike? The Merckx comes out looking better than I expected.