Really just seems like he didn’t like the running lifestyle and competition. If you want to maximize your talent in this endeavor, or any endeavor, you have to love what you’re doing. Personally, I love to compete and grit my teeth at the end of a race. He didn’t, and it seemed like more a job than something he loved to do.
Or maybe he didn't enjoy the lack of improvement.
It's exciting to train hard and go out and beat your PRs.
It is very hard to put in that same effort year after year without ever getting faster or placing higher.
And getting constant nagging injuries sucks.
His PRs were set in 2010.
He gave it 7 more years. That's not giving up easily.