I'm young enough (born in the late 1980's) that during my entire time in the work force, I feel like I've only ever met ONE "real" manager. I've known many people in management roles, but I think we've definitely lost sight of what good management even looks like. If you're under a certain age, I wonder if you've even met a real manager before. From today forward, many of the people in management roles may never have met a real manager before too - how are they supposed to fill a role they've never seen before.
I think we need some good management role models, and we need to find a way to encourage people in management roles to grow to fill this.
I don't have any studies or hard facts to cite, but consider this - I feel like part of the role of a manager is to bear responsibility and deadlines, manage the workers and give them the access and tools they need to succeed. But what I see most often is managers (not doing the work) acting like slave drivers, pushing all of the responsibility and pressure of meeting the deadlines on the workers to stress about. I see lower level workers staying late after work, taking 'ownership' of their manager's responsibilities out of fear they will get fired. That's not what it's supposed to look like but unfortunately for most millennials it seems to be the common experience.