Democratic rejected Kamala resoundingly in the primaries, and then the Democratic leadership tried to force her down everyone's throat. That's on them, not the voters. They asked people to eat a sandwich some shit on it instead of a shit sandwich and not surprisingly voters weren't too enthused.
No, it's on the voters, 100%. A primary would have been messy. She may not have been everyone's first choice, but she was 100% the responsible choice. People screwed over the country out of spite, but that's 100% in line with how immature and uneducated the US population is. Not to mention bigoted in various ways.