I think it's because designing good user interfaces is hard and very time consuming (at least for me it certainly is). And generally Linux users are more contempt to put up with inconsistencies and annoyances because many probably don't care and leave most things in a default state, or customize stuff to their heart's desire.
I'm not saying this is exclusive to Linux distros, I sometimes find the UI in Windows 10 to be confusing, having to jump between the settings and control panel application to find some niche option. It's apparent that parts of that UI were made 20 years ago while others are made with modern toolkits.
I hope that System 76, being more consumer oriented than other companies that mainly develop for Linux, listens to feedback from a wide range of users and manages to develop an ecosystem to be the "MacOS of Linux workstations" in the sense that everything is polished and working out of the box and everyone from regular home users to advanced professionals and enthusiasts can pick up and use without major inconveniences.