I tend to think this is the answer--the player type. The Rams have players so experienced they likely coach themselves.
If I am a young coach trying to make a big impact with ideas I think are powerful, I would probably be after players that are more impressionable.
With the Rams, McVay is driving and has Stafford and Kupp as his co-pilots. Great learning experience but I imagine input and the ability to create change is limited.
I'd like to see McVay hire someone from complete outside his circle and offensive system/style. Someone to challenge his ideas and create hybrid concepts stylistically. At a bare minimum, someone to call out the ultra predictable play calling in certain situations. 2nd and two, anyone not know exactly what McVay is calling in this situation?