I doubt I will EVER understand the thinking of MLB managers.
Jordan Zimmermann, in his first start after yet ANOTHER DL stint, had a one-hit shutout (on only 63 pitches) thru five, and got pulled!! I suppose it was precautionary (first start back from DL), but come on! A pitch count limit of 90 maybe, but 63??!!
I think you said it when you wrote "ANOTHER DL stint". Unless things chge drastically, the Tigers are looking at the 2020 season.
My understanding is they are not even looking at the 2020 season, but the 2021 season AT THE EARLIEST.
With his contract, they have no hope of trading JZ. They just hope he can be an 'elder statesman' in the locker room for the younger guys (and they DO have some promising arms in the minors).