Who objects to Sanders the most? Often times, it's the wealthy and powerful.

https://fair.org/home/maybe-rich-liberals-dont-hate-sanders-because-they-fear-he-cant-win-but-because-theyre-rich/

For the wealthy, ideology simply doesn’t exist. No, they’re just Very Concerned about fielding the Best Candidate.

Because it would be unseemly to suggest a group of super-rich hedge fund managers, Hollywood producers and CEOs would dislike a candidate who has made a career out of promising to expropriate the bulk of their wealth, we get a faux pragmatism argument. But polls show Sanders defeating Trump with numbers comparable to any other declared candidate—a fact the New York Times never bothers to mention, letting the idea go unchallenged that “socialist” (!!) Sanders is an electoral liability. The simpler, less altruistic motive is simply never entertained.