My off hand theory (not prediction) is that they picked unlikable Kamala because she is expendable.  Next month Kamala debates Trump.  If they got a bomb in it would take out both of their problems and not look like a political attack on their opponent like the botched Trump assassination.  It would be easy to blame on someone like Iran or Russia which would also further their international aspirations.

I have no proof of this, but it makes sense enough that I wouldn't be attending the debate even if it was in my town and free.