That leaves the unwashed middle, call them independents, perhaps moderates, certainly the non-affiliated. Those basically peeved at both parties and how both parties govern for only their base and not America as a whole.
I think you are projecting your own studied independence on The Independents. I bet most of them have little awareness of politics, and just vote for celebrities or the snappiest dresser. Those who think a lot about political positions and lament partisanship are a very small minority. Lots more sports fans who would rather watch ESPN than PBS. They are easily manipulated by demagogues like Trump with "simple-but-wrong" catch-phrases. Trump had to practically destroy our democracy to lose their support. If he had been just a bit less blatant, he would have won in 2020.