Stupid question (I'm a hobbyist Linux programmer): When do people use X and Wayland instead of an UI framework such as QT?

I guess it's obvious that people who create and maintain QT and other GUI libraries definitely use X/Wayland directly, is there anything else?

By "use", I mean it's the windowing subsystem on my desktops. I don't use it as a GUI library. I tend to use QT for that.

Oh I see, thanks. Guess I mixed up the concepts.

Qt*

QT == QuickTime.