Be highly unified, which eases software distribution. With Windows, the system software at least is from a single vendor. You’ll have differences in hardware and in versions of Windows, sure. But then compare that to Linux, where Wikipedia estimates a thousand different distros. Granted, a lot of those are member of families like Red Hat or Debian that can be supported relatively easily. However, others use more exotic setups like Alpine, NixOS, or Gentoo. Projects like Flatpak are working on distribution mechanisms, but they have their own issues. And even if you get it running, that doesn’t mean it integrates well into the desktop itself. Wayland should improve that situation, though.