Because any choice in a two party system is stupid to some degree, for most people. Most people’s beliefs don’t all line up exactly with one political party or the other. So every election is a compromise: which of your values must you prioritize? A whole lot of Americans aren’t doing well economically, they haven’t been doing well for decades, and under Biden they saw everything get more expensive. So they don’t like either side, and if you can convince them to vote, it’s only going to be for change. Kamala didn’t portray any change from Biden, so she lost.