I'm really not sure I understand the rationale here. The Dem field is already very crowded and it's pretty late for a new candidate to start up. Yes, he has good name recognition, experience, and a ton of money, but he also had some controversial policies during his time. Much more interesting would be if he ran as a Republican (as he did when he was NYC Mayor) because that field challenging Trump is incredibly weak right now. Some of the political pundits I listen to also argue he should just buy Fox News and de-radicalize it, not sure if that'd be helpful or just lead to everyone watching a different network but an interesting idea

These billionaire politicians need a reality check about the viability of beating Trump and especially from the left. Bloomberg would lose a significant amount of progressive voters just by nature of his extreme wealth, he has controversial past with policing policies that targeted minorities, and his main policy outside of stop and frisk was a soda tax. This is a vanity project not a serious campaign for president.