Motivations for Endorsement

Almost all of the democrat candidates for US President this year have terminated their candidacies and have endorsed Joe Biden.  Why?  Is it to conserve their war chests of campaign contributions for future use?  Why are they allowed to keep contributions in the first place after the campaign for which the contributions were made is over?  Is it because they actually do not support Bernie Sanders' agenda?  Why then were they parroting most of it throughout the past six months?  Is it because they do not think Bernie Sanders is "electable"?  Why did they imagine that they themselves would be, running as they were trying to outdo each other in speaking like a potential VP for him?  Is it because they don't think Joe Biden will last four years in office, let alone eight, and they'd like to be his VP so they can eventually have the office?  Bingo.  Bless the opportunists' pea-pickin' hearts.