I don't know why everyone thinks this is some rarely understood point. I think most people get this.

However, You have to be electable to a country where 30 to 40% of people. Think Trump is a god king who can do no wrong and never lies. Hillary's administration almost certainly would have been better than Trump's. Hillary still lost. Biden running as he is now is dangerous. That's where it makes the real difference. Biden might lose to trump and we might get Trump again. Any other sane and half way competent milk toast politician won't have that problem. Biden continuing to run is a danger to democracy.