Why do some want to get rid of GTK2 and all applications that depend on it?

We're up to Windows 11 now; the overwhelming majority of the devices sold with it have touch screens.

> We have a lot of applications that are designed for being effective with a mouse, and are not going to be redesigned. They work for those who use a mouse. Why is there the drive to get rid of them?

You mean besides the fact that the overwhelming majority of devices sold for the past decade lack any other input mechanism other than a touchscreen, and even if you plug a physical keyboard+mouse into one, they can't run those applications anyway?

> X11 fonts (bitmap fonts, not faces) come in 75dpi and 100dpi sizes (and that has already been so around 1990, i.e., long before GTK2), and I can tell every application instance which font it should use. And I certainly had 107 dpi on my laptop screen (1024x768 on a 12" screen) and ~10 dpi on the 120" screen that the projector displayed on. I did not need $deity, it all worked fine.

Your projector and laptop screen both claimed to be 96dpi as far as X and all of its applications are concerned. Change that at your own peril; nearly every X11-native application will break because non-font elements will not scale, resulting in text that either overflows or is truncated by its bounding box. (most notably in menu bars, single-line input forms and labels). Ironically the applications that don't horribly break bypass X11 font rendering (along with most other X11 primitives) entirely, relying instead on client-side rendering and just slinging the resultant pixmaps to the X server. (In other words, the same paradigm that Wayland is built around)

> Such units may be a good idead if you have a clean slate, but if you have a legacy of applications to support, then the idea of applying a scale factor to UI elements looks better to me (and I have seen options for setting such scale factors in various GUIs).

Congratulations, you just answered your own question about why toolkit APIs needed to be restructured. And again, there's not currently a way to have X11 apply a blanket scale factor on an application-by-application (much less element-by-element) basis.. because dpi is a global, immutable attribute.

> Experience tells us that GTK4 and Wayland will be abandoned when the next shiny cool idea comes around.

Experience tells us that GTK4 will be directly supported for at least a decade, and closer to two. Meanwhile, while Wayland won't last forever, it will remain relevant for at least the next two decades due to numerous long-support-lifecycle industries (eg automotive) basing their software stacks around it.