Agreed that GUI is a huge part of it, but I'd say for a different reason. There are almost no UI/UX designers contributing to open source projects. At the very

Agreed that GUI is a huge part of it, but I'd say for a different reason. There are almost no UI/UX designers contributing to open source projects. At the very least the ratio of them to programmers is incredibly low, far lower than at any company whose main product depends heavily on its GUI like office or graphics software. OSS GUIs are exactly what you get if you leave it completely up to an army of pure programmers (whether well-paid or not).