The post above yours pretty much answers it. There is also the fact that Detwiler is a FA in 4 days and Fry is controlled through 2023. Fry is nothing special, but he's a solid middle reliever. You don't punt a guy like that to keep Detwiler around for 1 more appearance before he leaves for FA. Had Detwiler stayed, he's, at best, the 4th left handed option out of the pen behind Bummer, Crochet and Rodon, so like...yeah, he didn't really have a role on this team anymore.