Big updates are secretly reinstalls of windows, where everything is dropped back in. Big, slow hard drives make this take longer.
Windows installs and reinstalls take hours more often than not -- just logging in for the first time on an up-to-date Win10 laptop recently took 10 minutes to "personalize" it for me ... and this was on an SSD. I used to have curiosity about how they made it so bad, but these days I've placed anything windows under a SEP field.