For conservatives, Trump was the lesser of two evils.
What worries me is Biden's "perceived" diminished capacity. And even though the country might be ready for a black woman president, Harris doesn't instill confidence.
The non-voters you mention may be choosing to throw in the towel faced with the choices.
Selecting Harris for running mate was a successful political chess move. It appealed to anyone wanting to see some long-standing wrongs righted. But I don't think it was well thought out. It could be called the Harris hangover.