Perhaps that's because Biden is a good guy while Trump is a malevolent narcissistic psychopath who will say or do anything to further himself to the detriment of anyone and everyone? Just a thought.
Biden is a "good guy" only in comparison to Trump, which isn't saying much. It may be enough to get him elected, but it doesn't necessarily mean he'd be a good president or a good candidate for president, other than in comparison to Don.
It's sad that this is the best that anyone can attract to run. Anyone that truly is qualified for the job is smart enough to realize they don't want it. A truly sad state of affairs.