In the march forwards, e.g. GNOME 2 -> GNOME 3, there are a number of regressions mixed in with the improvements. I think tackling overall UX may be seen as unattractive work compared to tacking on new features.

For example, GNOME Files (formerly Nautilus) and the GTK file chooser are not even as good as competitors from the 1990s (like the Mac or Windows equivalents). GIMP and Inkscape are also noticeable steps down from the equivalent software we used in the 1990s (not just the well-known Adobe products, but also products from Corel, Macromedia, etc.)

My impression is that the Linux desktop is playing catch-up with the Windows and Mac desktops, but since Microsoft and Apple have better funding it’s an impossible job—the target is moving too fast. In an effort to catch up with modern UIs, features that used to work are getting broken or the UX is degrading. The GNOME 2 -> GNOME 3 switch is just one example. I’m not saying GNOME 2 is better than GNOME 3 overall, just that large-scale changes are moving too fast and the polish and long-term fixes are coming too slowly by comparison.

Linux is usually my primary desktop and when I switch to my Mac it feels like a breath of fresh air.