As should be clear from the screenshots, in the 80's and 90's we were entirely unable to perform without gradients everywhere. Even my school notebooks where full of pencil- and pen-drawn logos full of gradients. At least one submitted essay had a heavily gradient-laden front page.

More seriously, most of the scene were teenage boys who were playing, not doing serious work. While some of the tools were mostly productivity focused (e.g. the assemblers, trackers), perceived cool-factor outweighed productivity for a huge proportion of them.

For the trackers in particular, while there were still the embossed metallic look and sometimes gradients, the dense UI is largely a factor of small screens (often down to 14" monitors) and very low resolutions giving you very little to play with. And the thing is, while it's messy, everything is there on one screen, and almost every tracker followed almost exactly the same principles and layout, so you learnt quickly enough.