It made objective sense to pick the primary’s VP choice over any other candidate, for fiscal and logistical reasons, but it was never a given. Biden could have had suspicions, or spite, or just been too battered to do the sensible thing. And even then having one or more party luminaries pull the reins could have thrown everything into chaos. Chaos was staring us in the face. It’s the narrative the GOP and press wanted, and it was a high probability.
Which is why what’s happened is astonishing.