I agree, especially for seldom-used Windows machines. The updates take so long, it's hard to imagine what they could be doing.
That said, Windows actually has real file locks so it can't update libraries and executables that are in use, unlike Linux. And I have recently noticed Mac OS updates taking a long time at bootup as well, the last one took 15 minutes, I assume because of System Integrity Protection--granted it's very rare unlike with Windows.
I simply don't understand why Microsoft can't do what Linux and the BSDs (including macOS) have been doing for years; no matter how big the update, it can be done in the background and only requires one quick restart to complete.