The problem, in my opinion, isn't that they "do", but they "can". Once the windowing system gave up control, it disempowered the user. For example, allowing apps to change the window chrome. For me that was basically the end of usability of WIMP. We no longer have a strong separation of concerns. we need that back, and we need the user to be in charge of the behavior of the windowing system. my strong preference, for example, is that I cannot interact with any window that doesn't have focus until I give it focus. At some point in the last 20 years, that standard was broken, and I have been stuck ever since accidentally doing things to windows that don't have focus.