I didn’t actually think they would run Biden.
Everyone on this thread presumes that Joe Biden will be the Democrat nominee. Many are presuming that Harris adds nothing to the ticket and would only lead to a Biden defeat. Everyone who has doubts about the viability of Harris should rethink the idea that Biden will be the candidate.
Picking Harris could very well indicate that Biden will be dumped and someone else will be substituted. If that is the plan, then the choice of Harris might make sense.