I couldn't offer any reason our case counts would peak and drop short of a vaccine or lock down. I don't know why we had the ebb in Aub/Sept really either.
The new strain idea is plausible though.
Only reason I can think of is that the 2nd wave scared everyone, and caused them to modify their behavior. Obviously I have no real evidence for that than just my gut feelings, but I got the sense that people hoped we were through it after Mar/Apr, and then realized with the 2nd wave that it was coming back hard.
Just from a "public opinion" point of view, it doesn't seem that the 3rd wave is scaring anyone into modifying their behavior. My gut feeling from people I interact with is that they're just going to chance it.
New strain might be a possibility, but I don't know if that Spanish strain hitting Europe has made it over here?
could school openings and football both pro and college have anything to do with it
plus catching it from Europe maybe
I don't think K-12 school openings have necessarily caused much. Obviously it's hitting colleges as living-on-campus student behavior is a lot harder to regulate than K-12.
So far it seems that the crowds at football games are limited and pretty observant of social distancing. My worry was that college football crowds would all be jammed into the "good seats" by the second half of games, but so far it seems they've policed that pretty well.
My belief is just that collectively we as a society are not particularly vigilant any more. We've grown tired of it, and are just throwing up our hands and saying "I'm going to do X and what happens, happens."