Cool designs are harder to scale to your 4K needs, we can scale the game itself because it is rendered or in other terms mathematically defined, it is easy to scale you essentially just times each vector by the scale you want, but with raster images such as in textures your only option is to increase the detail or take a better picture, now the UI if it was a raster image even a 4K one the size would be negligible compared to the size of the textures so that obviously isn’t the problem the problem is creating a new UI for every single possible type of resolution and aspect ratio, if size was the only factor this still wouldn’t be a problem but remember we are talking about scaling and scaling a raster image is much harder to do without losing detail or stretching it out so instead we use svg(scalable vector graphics) which are mathematically defined just like the game itself, now the question was why do we like boring UI? So why can’t we just make an SVG more appealing, well some shapes simply don’t lend themselves to proper scaling, infact anything that isn’t symmetrical will be distorted in one way or another, this greatly limits our design choices unless we want to stick to one aspect ratio. Otherwise mathematically defining a shape is simply a lot harder and more time consuming than drawing an image especially since the player usually just wants it out of his way so he can play the game.