I hate hearing stuff like this because it's all such conjecture and hard to verify. Personally I always thought Goff was plenty mobile enough for this offense. In fact I always wanted him moved around more.
Work ethic, accountability? Just have to say there never anything brought up about that in his 5 years there. Was he misinterpreted for being the "laid back California kid?" Maybe. He went to those Tom House QB camps every offseason which I always thought was a positive sign. I do recall Jourdan R. on the 11 Personnel podcast this summer saying part of this year with House was Goff hearing some feedback House had collected from coaches and players that "he might not have wanted to hear but needed to."
Football IQ? Maybe that was it, really. And not about 'intelligence' but just a requirement to process and read things faster that just wasn't happening.
Again just speculating myself. I like Goff a lot. Wish him nothing but the best.