I don’t have much understanding of the internals of the immediate mode renderers, but I think there are optimisations to only redraw regions where component inputs have changed.
You typically have to implement those optimizations yourself, and most people don’t. It’s outside the scope of the renderer in most cases for it to decide what should or should not be rendered. As a result, immediate mode GUI, while fast to develop, typically really kills a battery life on mobile.
