Trump's policies were very popular. Trump, less so.
Same with Biden. Democrats largely like the job he'd doing, and let's be honest, while I don't like the job he's doing, Biden's fortunes have improved among Democrat voters. That doesn't mean they want him to run again. Mostly, they're worried about his age, his scandals, and the growing acceptance of Biden's senility that has become harder to deny.
Voters can be funny this way. They like the policies but not always the person whose name is attached to them.
Makes sense...thanks.