Because some people struggle to do even that...? And because it does more than just tar the OS - it formats the filesystem, insmods the various modules, mounts the mount points and tar's rootfs. And it also upgrades to Sardine if you want it to.

Once all the pre-reqs are in place (which only need to be completed once per flash) and the script and tar have been downloaded (again once per flash), the user only needs to running the script in sequence (0-4 or 0-6) whenever they want to clone the OS. No need to remember each individual command/step or cut&paste from the wiki. Seems simpler to me...