My theory - I believe that BigTech started releasing huge updates to normalise having an always-on internet connection during updates and normalised the slow up

My theory - I believe that BigTech started releasing huge updates to normalise having an always-on internet connection during updates and normalised the slow update process for the opportunity it provides them to mine and analyse all data on your computer. Often an update is the only time when they can (and do) reset and toggle all the privacy settings back to their favour, and then do on device analysis (like collecting meta data of all your files or analysing your photos etc.). They can then send the data back to their servers to add to your profile they have on you unencumbered (no pesky application firewalls to deal with it). That's why I always make it a point to immediately switch off my router after downloading an OS update and starting an install. (Both Windows and macOS spend a lot of time in indexing your files - processes which can also be done post-installation - and doing all sorts of on-device analysis on your files to provide some specific feature, for example facial recognition on photos. And both collect a lot of your data during this process.)