Senior managers don't have the bandwidth to manage line engineers, if the engineer is doing what you say middle managers fear they would be peering with the middle managers to organize across their projects, eg a staff or principal engineer. You can easily interview for that skill set. It's also a reason to have a senior outsider on hiring loops to detect when you have these types of managers.

If the manager are actually attempting to do this pathological move, a staff or PE will notice and work to correct that issue with senior management. Otherwise engineers leave as it removes their growth areas.

At least at non-pathological places.