It’s because she wasn’t a major contestant in the 2016 primary because people voted for better candidates. Also, she seems to be a 1:1 copy paste of Biden, which isn’t good because people didn’t like Biden half assing his promises in office and giving republicans an easy time making a counter campaign.
On top of that she basically told the uncommitted group to get bent, so that gives Trump more voter leverage similar to how he beat Hillary.
Biden was met with the same voter response because he was voted in explicitly to remove Trump. Otherwise he’s known as being Obama’s VP, of which even Obama said that he should retire afterwards because he was a centrist.
It’s the same deal as 2016, where the DNC thinks campaigning on “lesser evil” is a viable strategy in order to retain their lobby money. If the RNC actually had more than two brain cells, they could easily win this election by having their candidates not act like insane asylum criminals.