It’s not really about Xeyes, at least not only about Xeyes – think of Xeyes as a demonstration of what could be done. Getting global screen coordinates is very useful for countless other tasks regarding UI automation.
And it’s not just a frivolity, it is actually has a use. Like I said, it helps me find the mouse pointer on multiple monitors, since I have blind spots in field of vision and severe myopia. But again, Xeyes is not the main issue here, it’s the inability for me to easily get the global position of the mouse, to easily detect and emit keypresses globally, etc…
Thinking about X11 being phased out in favour of Wayland gives me anxiety, everything is so locked up, your own desktop does not even let you program a keylogger. I should be able to do that if I want (and suffer the consequences if I’m not careful). The whole philosophy of it treating the user as too stupid to be trusted with global position of the mouse cursor, I find it defective by design.
What I really want is an ability to write a program in C in less than a couple hundred lines of code, that emits and listens to keypresses, moves the mouse pointer around, clicks on specified coordinates, gets information about windows, etc… Xeyes is just a very familiar and iconic symbol of that.