Some of it is 100% misogyny, I think some of it is also that 4 years ago the country was literally on fire in a lot of places and Trump was obviously to blame for a lot of it, so it didn't matter so much to apathetic voters if Biden's messaging was weak. Kamala may have won then too, though misogyny would have made it closer. Now the country is much more stable but still not great, but Democrats are in charge and therefore obviously to blame, so people who largely haven't been affected negatively by the Republicans (e.g. men, especially non-desperately-poor white men), are apathetic again