The common thread thru all the OCs, assistant passing game coaches, whatever, is Fisher. Fisher believes in Martyball, the blend of power running and horizontal passing that was able to have good regular season success but always failed against better teams in the playoffs. So from the start it's a losing philosophy. Then you add that the gimmick of the west coast offense has mostly died out and now the most successful teams in the NFL mix their short passing with vertical pressure on a defense.
I am a Pac12 hater and never particularly liked Goff due to the air raid offense and bad defenses he faced in college, but nevertheless I was downright giddy when the Rams traded the farm to move up to take him. Because more than Goff himself, it seemed to be a clear signal -- combined with hiring Groh with his Gase background -- that maybe, just maybe, Fisher had changed his ways and was willing to entertain a more vertical concept. A terrible rookie making mistake after mistake but at least trying to push the ball downfield was going to be a 1000% improvement over awful Keenum employing Fisherball's ceiling of 7-9, because the vertical threat would open up the entire offense for Gurley and the short passing to be that much better.
Then when it became clear that the "Keenum's our starter" thing was more than just a stupid "earn it" motivational game by Fisher, the reality was a slap in the face. It has nothing to do with Keenum, because everyone knew what he is -- it was the signal that Fisher isn't going to change his stripes. Settling on a "game manager" QB because there's no better option and still maintaining you can win with him is admirable. *Wanting* a "game manager" QB because that's your preferred offense philosophy is simply inexcusable, and Fisher has run out of excuses.