These are not the only two things, but the main reasons:
1. Personally he is a narcissistic pompous ass with no filter between his thoughts and his speech/tweets. Women and a lot of men don’t want any more of this even though his actions politically have improved the lot of every American citizen.
2. His Covid response, although probably in results was as good as any President could have done, gave inconsistent messaging about the seriousness of the disease and he abandoned a Covid “task force” that could have kept messaging on track even though it would have had little impact on actual infection rates. It was the actions of Governors, not Trump, that collapsed the economy and made people jobless, and it was the actions of Pelosi that kept necessary Covid relief money to really help unemployed and small business owners without massive stupid pork and corruption. But Trump got blamed, not that he didn’t deserve a little.