I have heard from people in the know that Hall has had some nagging injuries for the past 2 years and others have posted that here. That can wear on a person and make them question their coaching and training. As an outsider, I certainly would question running 3 world class marathons in 1 year. That appears to have been the beginning of his issues. Then he continued to run 2/year with these nagging issues.
This year he ran the Tioga Pass run a week before Philly and then ran sub par in Philly and pulled out of Chicago. Either he or his coach should not have allowed that. There is a problem here that either he is not being reigned in by his coach/team OR he refuses to listen.
Unfortunately, 99.9% of the people talking on the message board don't really have any insider information about who made these decisions. The .1% are not giving details if they really are the .1%.
Time will tell if this is a good decision for his career. I hope it is.
BTW, Sara Hall has had a very good year in contrast to Ryan. I hope this works in her favor too, but she seems to be leaving a situation that has her on the upswing (after some longer term flatness).