It's one thing to choose Bloomberg over Trump, but quite another to choose Bloomberg over one of the remaining Democratic hopefuls. As a choice among the current Democratic hopefuls, he is the most Trumpian and the most Republican. Choosing him moves the Democratic Party to the Right of Reagan. If he truly wanted to do the courageous thing, he'd run as a Republican or as an Independent Conservative.
Defeating Trump really isn't his main goal though, it is defeating Bernie. He wants to maintain the Reagan era by shutting out the Left from the Democratic Party, at least more so than it has already been. This would result in a rejection of the growing young Democratic Base whose ideologically aligned with more Traditional Democratic sensibilities.
The important choice right now is in what you want the Democratic Party to be. Do you want it to be Traditionally Republican? Traditionally Democrat? Not Trump?
1) Why not just be a Republican then?
2) Then choose based upon who reflects those principles and not on some notion of "Electibility". aka, have the nads to stand for something.
3) This is the stupid choice.
People want to choose someone who has a Vision of where they want to lead the nation. Biden is failing because he did not offer this. Bernie is succeeding because he does offer this. Bloomberg is still somewhat an unknown factor, so far he has risen on the back of the most massive propaganda campaigns in history, but that could change quickly once he hits the debate stage and others begin responding to his campaign.