One reason why Goff is not ready is that Fisher wants to run his system, and not adjust to the player, same way he did with Quick.

There apparently is no flexibility. If we needed to start Goff tomorrow, why not implement some spread formation stuff that he is used to?

And if Quick is dumb, then create some plays that he can run.

But using the Quick analogy, Fisher's stubborness means that 3 years later he is still coming along.

I'm guessing he will do the same to Goff.