I did not see that last summer during our Florida to Idaho and back via Hwy 2 and down thru NE and KS back to FL. 21 states, 33 camping spots and we got turned down once on a last minute call to a park. And that was right outside West Yellowstone. And our second call got us a spot for the night.
My belief is that this over crowding occurred in states with lockdowns that shut down state parks and restricted the number of campers allowed in private parks. So yes that caused local overcrowding.
Now some boondocking sites seem to be mobbed but since we had never been there before I cannot say if that was normal. A great boondocking siye outside YNP was packed but YNP closed almost all the park cg.