Fedora also wants to reboot to install (dnf) updates offline, as I understand it's to prevent potential instability from running processes getting confused when their files get swapped out under their feet.
It's also good since you can't swap out the kernel without rebooting.
I assume Microsoft took the same approach, just replace everything offline then reboot into a fully up-to-date system without any chance of things in RAM still being outdated.
