Why did the "Biden is Dems best / only chance to win the election" crowd shut up after he was replaced by Harris?

Especially those who thought he was their only chance to beat Trump, why did they shut up / join the losing team Kamala Harris when Trump is totes going to win now that he is up against Biden?

Why did the "Biden is Dems best / only chance to win the election" crowd shut up after he was replaced by Harris?
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