Interesting. I hadn't thought of it that way.The thing to remember about LCARS was that at the time it was developed the "windows" paradigm hadn't really taken hold. (yes, yes, I know the Mac was up and flying by then) Most PC users were still confronted with dos based programs with rudimentary graphical interfaces. Wordperfect and Lotus 123 both used basic black backgrounds with solid color interfaces. the idea of button graphics painted to look 3d was not really out there yet. So, LCARS is an extrapolation of what we were used to then. Black backgrounds with primary colors. To make it look "futuristic" the designers rounded all the corners and tried to apply a workflow methodology to the layouts.
One big reason LCARS looked so futuristic is that it employed smooth curves and typography, as opposed to the 'pixelated' look of computers at the time. Interfaces using smooth alpha-blended curves weren't fully realized on actual devices until this decade. (e.g. things like the iPhone.)
Had they used real computer technology, the look would have become quickly dated and "Atari" like. As it was, LCARS has held up pretty well visually to modern eyes.