I think it's just that Rust doesn't have inheritance/subclassing as a feature. As a result you have to do all sorts of mental gymnastics with impls and macros t

I think it's just that Rust doesn't have inheritance/subclassing as a feature. As a result you have to do all sorts of mental gymnastics with impls and macros to fit Rust interface on GTK, while with other languages subclassing just "works". I also think this is why Rust has lagged heavily on the GUI development front. No matter how you claim component or ECS-based architectures are better and faster, sometimes the only thing you really need might be a good ol' inheritance-based scenegraph... You can definitely do UI with a component-based object model (ex. Unity game engine), but the whole process seems a bit more... convoluted.