According to a Maureen Dowd opinion piece in the NY Times, it turns out that back in 2018, Obama told Bernie that he had to sell out in order to win the Democratic nomination. Bernie didn't. We saw what happened during the campaign. Everyone bowed out and endorsed Biden with Obama's urging.
I bought in to the "Hope and Change" when Obama won the presidency. As time has gone by, I have really seen the ugliness in Obama's politics and realized that there was no change at all. This is also why I gave up being a Democrat years ago.