You will notice that the total number of "group starts" increased every year until 2016, when there were approximately 440 fewer start groups than in 2015. I have a good idea why the count for North Carolina (NC) decreased by approx 130, being almost entirely due to two frequent riders being knocked off the road and their corralling of others to ride once or twice a week going missing, combined with two other frequent riders essentially retiring or at least taking a hiatus. However, I have no information or knowledge about why California (CA) and Washington (WA) also showed significant decreases in their counts. Guesses would include a post-PBP effect and perhaps a decrease in K-Hounds in those states.
I'm attempting no profound insights (at this time); just simply showing the high-level information.
I have not attempted to look at the amount of brevet riding by year / region or state.
(*) "Group Starts" -- for purposes of this chart / blog-post, a "Group Start" is one group starting one perm or perm-pop route (presumably at the same time, though I cannot confirm that same start time assumption), regardless of how big or small the group.
The 40-plus-thousand "group starts" in the above chart translate to approximately 68-thousand individual completed rides / "RUSA-T" certificates. [Obviously, there is a lot of solo riding occurring on perms. Hey, I like doing solo bike rides, but it is rather amazing the amount of solo rando perm riding that occurs.]