Because he supported things they disagreed with, as did I, and many millions. They also don't believe that there won't be another election. They didn't like Kamala, and if the DNC keeps forcing unwanted candidates on the electorate, maybe they need to face the consequences of doing so.

They forced Hillary on the electorate instead of Sanders. They then forced Biden on the electorate when there were half a dozen better candidates. And then they forced Kamala on the electorate.

They didn't vote because at a certain point, they gave up.