There are technical reasons, although in practice I'm not sure how important they are: Game engine UIs are usually immediate mode, which means everything is re

There are technical reasons, although in practice I'm not sure how important they are: Game engine UIs are usually immediate mode, which means everything is rerendered in the game loop, 60 times a second or so. Dear IMGUI is the most well known example but I think Godot works the same way. Other UI systems (the web platform being the most famous) are event driven. Which means there is a loop, but it's just listening for events like mouse clicks or timers, and the UI is only redrawn when something changes.