They just have some terrible contracts weighing them down. The Carpenter contract extension after the Goldschmidt trade was a real head scratcher for me. That ties up a lot of money in an aging 1B playing 3rd with a bad shoulder who's having a harder time staying on the field all the time. I love Carp but I thought he'd make some good trade bait for a young arm from an AL team looking for 1B/DH help in the offseason.
I'm not sure Fowler can come around to make his contract palatable. I hope he can finish strong enough that maybe we can get somebody to pay half the remaining portion after this year...assuming you can get him to waive the no trade. We've got to get Arozarena up for an extended look at some point...maybe at the expense of Bader in the short run.
I'd gladly go to sell mode this year to back build some talent but I'm not sure we have the pieces that are going to return any high level prospects.
I'd prefer to go to sell mode as well. As I've said before, even if they sneak into the playoffs, this team hasn't shown me anything that indicates it could get beyond the first round. They're just bad.
The problem, as you stated, is that they have almost no one left to trade. You want to hang onto the few players who are having moderately decent years (DeJong, Goldy, Flaherty, etc). You have aging players with albatross contracts (Carp, Fowler) and then young talent that is struggling (Wong, Bader). I could really only see them trading J. Martinez to the AL, but that has been rumored for 2 or 3 years now and no movement.