Also, why the hell does it need to reboot to install updates? Ubuntu et al don't unless you update the kernel, which 99% of the time you don't.
Because Windows has an awful filesystem, no sane concept of an init system and a laughable driver model. I'd love to blame the Windows Reboot Insanity on laziness but, architecturally, it's just not possible for it to update like a Linux/Unix machine. And, I mean at the fundamental kernel and filesystem levels.