Because he got worse for both teams the longer he played and DCs got more tape on him. And he ultimately got benched in both places.
Look, I think the world of JD and nobody wants for him to succeed more than me. And I would bet that 99+% of VolNation feel the same. He is one of the most-respected and admired players to ever come through the program. And it is well deserved.
He was a very good college QB, and did exceptionally well here…especially considering his coach.
And he achieved his ceiling last year IMO. He went from 3rd or 4th on NFL depth charts and bouncing around to likely an established #2 with one of the league’s best franchises. And that is nothing to be ashamed of. I hope he sticks with the Niners for many years.