The average Linux desktop has never been fully standardized. The average Windows desktop today (let's say, W10/11) is descended from W7 which was arguably really consistent. Even if they took W7 and bastardized it by introducing 10 different design languages (Metro, Modern, Fluent, new Fluent, ...) there was something to build on top of. On Linux, there are some GNOME guidelines, there are some KDE guidelines, nothing really universal. As much as I dislike the general macOS experience, Apple got it right early on by simply forcing you to adhere to the general vibe of the OS