>>713337689I can't believe it took so many posts for the right answer.
The reason why all UIs look the same is because they have to follow guidelines to be usable by 999 different kinds of cripples, retards and invalids.
It's mandated by law in many """Developed""" countries and if the game is high profile enough, the developers can literally get taken to court by some sufficiently autistic cripple and lose if they can't prove they made a sufficient effort to accommodate them.
Diegetic UIs are seen as anti-accessibility so no sane AAA developer will risk because it makes them more vulnerable in court.