Q. Why has Windows 10 moved to a monthly Cumulative Update approach?
A. Prior to Windows 10 and Windows Server 2016 Microsoft would release updates monthly (patch Tuesday). Those updates were in the form of separate updates ranging from critical and security updates through to recommended updates and organizations would pick the updates they deployed. Many organizations would deploy critical and security updates but not other types of update. This means there are literally millions of different possible patch configurations deployed out in the world. When Microsoft performs testing they test on machines that are fully patched and its not practical to test against every possible combination which is why sometimes problems are found by customers as that exact combination was not use for the Microsoft testing.
To solve this Microsoft are moving away from a large number of separate updates each month to a single cumulative update each month. This cumulative update will include all the updates and because it is cumulative it includes all the previous months. This means to get current you just deploy the latest Windows 10 build and the latest cumulative update. This approach will remove the wide variation of patch combinations out in the wild.