No callbacks, so no forced heap allocation nor lifetime management . "oh you want to use FooGUI? First let me tell you about the object hierarchy and object lifecycle". No mvc. No custom, required data structures.

The programmer just copies and pastes from the demos, makes small modifications, and it just works.

(No offense intended towards your framework, I've used gtk, qt, and swing and have never understood them like I understand nuklear and dearimgui)