That’s not surprising. The Democratic Party as currently constructed is a third-way coalition including traditional progressives, labor, neo-liberals, and minorities. Sanders might have a plurality of the support in the party, but he threatens to blow up that coalition.
A successful Presidential candidate has to win 95% of their own party. But only 76% of Democrats say that they would vote for a socialist: https://news.gallup.com/poll/285563/socialism-atheism-politi.... A successful Presidential candidate has to evenly split independents—who comprise 30% of the electorate—with the other party’s candidate. But independents’ views of socialism are much closer to those of Republicans than to those of Democrats: https://www.npr.org/2020/02/19/807047941/poll-sanders-rises-.... Any successful democratic candidate must win super-majorities of non-white people (90% of African Americans, and 75% of Hispanics and Asians.) But just 33% of non whites have a favorable view of socialism.
Bloomberg isn’t “buying” the support of “media outlets, think tanks, and state party leaders.” These are the people who established the third way coalition after devastating losses in the 1980s. These people are already looking for an alternative to Sanders. Bloomberg’s money is just getting his candidacy out there to help coalesce the “not Sanders” majority of the party.