The So haven't given up on Barfield because he was willing to sign a minor league deal for low money and because, with Benintendi, Betts and Bradley, the Sox do not anticipate the need for any new outfielders for a few years. So they can dedicate the upper minors to organizational fillers rather that player development at that position. If the Sox needed a corner OF and had a prospect working his way up, they would bench Barfield to play him in a second.
He did hit 27 HR's at age 29 last year in a league where the average was was like 22 years old. He's not a power prospect. Or any type of prospect. He's not only not on the 40-man roster, it would take a score of injuries to get him there.
At this point in his life, Jeremy Barfield is probably playing because he loves the game and, as he is from a baseball family (dad Jesse had a good career in Toronto and brother Josh reached the majors in SD), it's really what he knows best. Good for him. But his future is very limited, and he does know it (hence his joke on Twitter about the Sox not getting Otani not mattering, since they still had him)...