We can both cling to our presumptions. Certainly there is a case to be made that they should have taken anything for him. But they can probably get the same return (i.e. not much) if they DFA him, i.e. about the same as Alec Asher (that trade has still not been completed right?)
It might not even be that bad though. He couldn't fetch a decent prospect at the deadline, but he could fetch a bench player or middle reliever (or be packaged w/ other players, or used to take back someone's bloated salary plus a prospect) in the off-season. He is probably still worth the 40-man spot, whether for trade purposes (if it can't be done before Rule V) or depth.
The fact that he was hitting better in July didn't really trade his value, any more than Rupp's high points changed his. Scouting reports go deeper than that, and in both cases the players' limitations aren't really about their bats, just whether their bats can make up for them.