Conspiracy theory time-
If I were trying to decrease the chances of Bernie getting the required number of delegates, I would want Steyer out (assuming the few African Americans that were voting for him are more likely to switch to Biden, Pete out (moderates more likely to transitional Biden), and both Warren and Amy to stay in for the time being to make it less likely that Bernie wins Minn and Mass.
Bloomberg is useful because he is railing against Bernie every chance he gets, but is so unlikable that no one seems inclined to vote for him.
I have not heard Pete or Tom endorse anyone yet, the smart move would be to wait until at least after Tuesday make sure they endorse someone viable.