Conservatives are more afraid of Bloomberg than Sanders. They used to be more afraid of Biden than Bloomberg, but Biden has since come off as a borderline invalid. Many are still more afraid of Buttigieg than Sanders.
Conservatives and conservative independents think Trump will beat Sanders and that it won't be close.
Aside from Bernie's always-angry demeanor and ideas that are coming out of left field, he hasn't proven himself to be particularly competent or effective. He's weak on the economy (even clueless), weak on immigration, and weak on foreign policy, which are all Trump's strengths. His main claim to fame is HCA, but that won't get through even a Democratic congress. His Green New Deal is a complete non-starter. Sanders and AOC are basically a meme for the angry and disenfranchised younger generation.
Once people scrutinize Sanders' ideological and political past, it will be way too easy to label Sanders as a radical and compare some of his base to Antifa.