You say his accuracy on deep hits declined. Why do you think that is? Generally speaking, people don't just get spontaneously wise at things they used to be pretty good at.
Here's an article with the meat colored charts on accuracy/passer rating from 2019 compared to 2018.
During his terrific 2018 season, Jared Goff was excellent in two areas: play-action passes and deep throws downfield. On play-action passes two years ago, Goff threw for 15 touchdowns and only two interceptions with a passer rating of 115.0. On passes at…
theramswire.usatoday.com
He was pretty damn good at deep balls in 2018 and 2017.
So given that you say he declined and that he used to be pretty good at deep balls, what's your theory for the cause of the decline?