I'm actually disappointed that this happened. Bernie was the poison pill that would've buried the democratic party. By winning, the party will turn into a fringe, niche party with views that the majority of moderates thinks is too extreme. By losing, the party would alienate a huge base of Bernie fans by making it look like the election was rigged twice in a row. By exiting, neither event happens. Just blame it on the black swan event...
Regardless, it's not like Biden would win the general anyway.