If I had to guess, it’s because of two things: windows creates a system restore point, which tracks every file the update touches, every time it installs an update (as opposed to something fast like ZFS or btrfs snapshots). Then it also keeps a prior version of anything system related on top of that, these outdated and insecure system libraries live on forever in the WinSxS folder. Imagine keeping an insanely bloated version of every system package installed, forever. I’ve seen WinSxS get to be over 80 gigabytes, of just old crusty shit.