@VamptVo so, it comes down to why some people withheld their support from Biden.
Especially in a tight election, groups like the Uncommitted movement have a chance to pressure a candidate to shift their position in order to win the group's votes.
It's a dangerous game.
Holding out too long can make it impossible to deliver those votes.
Announcing support too soon without concrete gains can also alienate group members, who might not come to the polls.