I think this is a side effect of the use of CBS since Vista. Back in the update.exe days, there was no database to maintain and most of the work was done in update.exe including adding a list of files to change on reboot into the registry, as well as adding registry entries for the updates installed. It was a fairly simple system. CBS now uses a database to keep track of updates that needs to be updated on reboot and is much more complex. Win10 actually improves the situation BTW by using single cumulative updates instead of multiple updates for each patch Tuesday.