"2) Or: Managers have too narrow of a view of what their job is. Speaking generally (not accusing the parent comment) - This often happens when developers who haven't experienced good management or managerial mentoring get promoted into their own management positions and assume their job is literally just to delegate to the engineers and then check on them until it's done. In non-stagnant tech companies, there is always more for managers to be doing: Reviewing/updating documentation, helping with hands-on testing of the product, observing or interacting with customers to get a deeper understanding of the problem, coordinating with the sales team to get a better understanding of their domain, and the list goes on. Many of these tasks aren't immediately obvious without proper managerial mentorship, and they might be downright foreign if your only experience with managers has been of the delegate-and-wait variety."

Big companies tend to hire "specialists" to do all those tasks you mentioned, which I think is a mistake. If the purpose of those tasks is to improve the function of product development, which can be rephrased as "make the coders more effective" then each of those people require a high bandwidth communication channel to the coders. You can only have so many people that you communicate a lot with, and so the effectiveness of those people in improving the effectiveness of product development is limited. Their job is to make sure the devs arent working in silos but they all just end up forming their own silos because its simply not practical to have high bandwidth communication with all these different groups of specialists.

Im talking about designers, product managers, project managers, user researchers, data analysts etc ...

My broader point is that I agree with your vision of what a manager should do but IME it's not how larger companies tend to be structured.