In fact I remember now that I have had a manager who followed this exact advice: they'd agree with you about what was right and wrong in private, but do nothing, or very little, in public. It was infuriating. I didn't quit over it, although I wish I had in hindsight; instead I stayed uninspired and frustrated and burnt out until the manager eventually cycled out for another. But my guess is the team was half as productive or less than it would have been if the manager had stuck up for them in public. There is really nothing as demoralizing as when none of the people with power stick up for you. Of course, they will say that they don't have power either---but that's the trick. Everyone up the chain says they have no power, they're just following orders; the decision making is abstracted from on high. It is always a lie: everyone has power; just, the power is proportional to the risk you take to use it. I should have threatened to quit over being treated better, and meant it, and the manager should have threatened to quit to their bosses over the same things, and everyone else up the stack.

(Of course, an organization where your only way of getting listened to is threatening to quit is already unimaginably toxic. A healthy organization has a moral code of its own: you should be listened to because you were mistreated, not because you had to threaten something to be heard. But this seems to be increasingly untrue in modern tech companies where everyone seems amoral and just does their job and tries not to rock the boat so they can get to their next stock grant.)