Biden was running on massive infrastructure investment, student loan forgiveness, ending the war in Afghanistan, child tax credit and a $2000 cheque in the mail . Harris may have had those in her platform as well but she wasn't mentioning it or Bidens wins on these at all, her campaign was "I'm not trump" and we learned from Hillary that's not enough.

Biden campaign was "build back better" a motto for change much like another democrat who actually won. Harris' campaign was "were not going back" which implies no change and relies on you thinking the trump years were horrible enough to justify the current status quo, and apparently the only thing Americans remember about the trump years was the economy was "better" and wanted to go back.