Per Chad Jennings of The Athletic:
(Barnes) had a 7.94 ERA through the first two months of last season before missing the middle two months with right shoulder inflammation. When he returned, the results were better — a 1.59 ERA, with many of his outings in a closer’s role — but the strikeout rate wasn’t what it used to be, and the Red Sox were not convinced that the underlying data suggested Barnes was on a path to regaining his past success.
“Probably not, unfortunately,” one evaluator inside the organization said. “Tough to say (why). Just wasn’t the same.”