Ubuntu focuses its efforts on ill-advised efforts like writing its own compositor (Mir) and Desktop environment (Unity).
Currently, most work to advance the Linux desktop is focused on a new project called Wayland (Used by Fedora for last few releases), yet Ubuntu has decided to double down on X11, a legacy project that clearly has no future and has issues like screen tearing that are basically impossible to fix.
Another tangible example related to developers: On Fedora/Arch you can run docker containers without requiring root due to Red Hat's work pushing podman forward, however you cannot do this on Ubuntu/debian because they lag behind upstream