If you look at 2020, the party and the media both waited to coronate Biden as soon as he declared. He had name recognition and he was Obama's VP and supposed best buddy, which yielded a lot of (I think unearned) trust from voters. Because of that, he could raise lots of money from traditional Democratic donors. There was also a lot of fear that only an old white man could defeat Trump given the white backlash to Obama, which shot down half of the primary field essentially from day one.