As an RBA and ride organizer: a 300k is significantly more work than a 200k, IMHO. A 200k is a day ride; you don't have to worry about finding late-night controls, overnight parking rules at the start/finish, finding a finish that's safe to wait at (as a woman organizing rides, this may be higher on my concern list than some organizers; the time I felt at most danger doing anything rando-related was being harassed while solo-working a control), etc. For regions with organizers whose houses make good starts/finishes, adding more long rides might be pretty easy, but it can be pretty challenging if not. A 200k with rando-standard levels of support (i.e. not much if anything) is pretty easy to throw together. A 300k starts to have logistical concerns.
Also, to put the numbers in perspective, for ACP brevets (the ones that already must be scheduled for 2022), the numbers for RUSA are:
200k: 211
300k: 132
400k: 92
600k: 71
1000k: 19
That doesn't look like a huge drop-off, it looks like steadily lower numbers of extra rides beyond a region's core series as you go up in distance. 47 separate regions are holding a 600k, at a quick count, so 47 of each can be assumed to be the "core series". Add to it the R-12 rides and the fact that it's not uncommon to run a 200k alongside a longer ride -- both Westfield and New England in your "area of interest" do that a fair bit, which pads the 200k numbers, and it's not much drop-off at all.
(note: I said "show only future events" when crunching the numbers, so if anyone did run a brevet this past weekend I didn't count it, but that should be a fairly low number.)