No, that is because X servers only provide the mechanism (window system, graphics, events, input, etc) but not the policy while providing functionality for the

No, that is because X servers only provide the mechanism (window system, graphics, events, input, etc) but not the policy while providing functionality for the clients to provide that policy themselves. So a window manager can be made with and rely only to functionality provided by X11. On Wayland the "window manager" (compositor) has to provide both the mechanism and the policy.