It feels kind of simple to me. Wisler just isn't good. I don't really think he's working on anything or something similar that could give us some hope -- that wouldn't make sense when he's competing for a job, even though we all know that competition is a farce. He's just not a very good pitcher.
And yet, he was the key return for one of the best closers in baseball. That's enough to make me nauseous.