If UAC is not enabled, the "Run as administrator" option does not work. Worse, I think it runs the script without any kind of elevation or any indication that it have failed to elevate. Other executable file types which have this option behave the same way. "Run with UI Access" runs the script using a different executable file, but again has no real effect. Without UAC, there are no restrictions for UI Access to bypass.
Fortunately, it's uncommon for UAC to be fully disabled on Windows 8 and later. I think disabling UAC (via EnableLUA) used to breaks apps and the Start screen. I'm not sure what effect it has on Windows 10.
In Windows 8 and later, setting UAC to "never notify" via Control Panel only turns off the notifications, not UAC itself.
The check also serves to avoid creating those context menu items on Windows XP and older.