I have ideas about writing a GUI framework [1], but why in the world would I spend the time to make it up to the author's standards unless someone was paying me?

GUIs are a lot of work. People should be more willing to pay for work like that. Wanting everything free is one reason Big Tech has so much control.

[1]: https://gavinhoward.com/2024/05/a-new-architecture-for-a-gui...