The thing that McVay preaches, and Goff carried out, was to limit turnovers. And with 28 TDs and only 7 INTs, he certainly did that. There's no better way for a QB to have his confidence shattered than committing a lot of turnover and losing a lot of games. I suspect McVay schemed to avoid that at all costs.
My speculation is that McVay is bringing along Goff in a controlled development process in the same way he brought along Cousins. Step by step. The game slowing down just a bit more each year. Understanding the reads quicker and better each year. Expanding the field and playbook a bit more each year.
In fact, I think a lot of GMs would say that this is probably the way to develop QBs, and probably the way many are; it just isn't talked about so openly. And equally so, I think many HC's don't know how to develop QBs, give them way too much to handle, and they fail and they never live up to the expectations.
The Aaron Rogers of today is certainly light years beyond what he was in his 2nd year....or 3rd......or 4th.
And since things have gone so very well with Goff, and he's proven to be coachable and has a lot of self control, he now has confidence. And now with this he can take yet another step. Perhaps this is just my hope. But I think it is a deliberate development track devised quite carefully so as not to ruin a very valuable commodity.
One of Goff's glaring deficiencies is that when he's on the run, he doesn't throw well at all. I'd bet he'll work specifically on how to throw better and more accurately outside the pocket, on off schedule plays. He has plenty of athleticism to do it; he just doesn't have the technique.