Yes, because others were making all the decisions and it was hoped that Kamala would appeal to some of the minority and more radicals bases within the Democratic party.
I fully expect that if Biden is sworn in on Jan 20th, that Kamala will within 2 years become the president because Joe either has to resign for corruption or health reasons or he dies.
2 years? I predict Kamala would be president six months after January.
Obama wouldn't get NEAR campaigning for Biden for MONTHS or more.. Then SUDDENLY he hits the trail for Biden. Hello Captain Obvious!