He’s unelectable because of his last name. The nation, right or wrong, does not feel good about that name; and there is more venom and slobber over that name than could be neutralized with an ocean of love.
He is also unelectable because he is a RINO.
And even if they did feel good about that name they do not feel good about giving a third person from the same immediate family the Presidency yet again so soon - that’s worth losing at least 5% of the vote by default, maybe more, but even that is enough to ultimately doom the candidacy as viable. The fear of a dynasty gives him a ceiling.