It’s not as simple as telling Devers “hey, your defense at third base is killing us, so we’re moving you.” I’m not entirely sure thats any better. And what happens if you tell Devers that, and then you still cannot get an upgrade? The Cardinals want you to take all of Arenado’s money and want Roman Anthony? Bregman prefers the Detroit offer? Do you then go back to Devers and say “about your defense and that new 3b, April Fools!”
(I do not think the Cardinals were that unreasonable. Just making a point that the deal could fall apart.)
And I seem to recall Bloom’s initial extension offer to Devers paralleling a contract that was signed about that time by Matt Olson, and the explanation was they envision Devers’ future at 1b. If that’s true, it has come up before. And it’s probably why Devers was asking about his future at 3b to begin with…