Goff was appearing to digress in performance with the fumbles and lack of crisp execution. I imagine there were several meetings between McVay and Goff over the matter, probably almost a daily thing and it finally reached a breaking point. I imagine Goff became just as frustrated, a couple words might have been exchanged at which point anger kicked in and it was over. Benching him for Wolford in the playoffs was the final straw for Goff. Considering his salary drain on the cap, it was untenable.
Speaking of which, we have all criticized the Rams for the large contracts but that is also an indication of taking care of your players and a willingness to set them up for life if they perform at or above expectations. I see that as a positive motivation not only for the current but also future free agents.