Microsoft is working on patching any exisiting flaws in windows 10, and that includes forcing you to upgrade your operating systems. Microsoft started cleaning up their operating system support list a while back with Windows XP, and has brought it all the way up to windows 10 with their windows release health dashboard.
Windows 10, version 1809 is 14 months old, forcing upgrades to 1909, which effects all home and pro editions and will take effect May 12th of this year.
The feature roles out with a "Download and Install Now" (DaIN), which forced upgrades from 1803 to 1809, and into 1903 of Windows 10 version. The DaIN allows users to choose when to upgrade their operating system, and even schedule it.
Most system and server operators waiting till the end of the support cycle of the current version before forcing an upgrade throughout all the systems, bypassing the DaIN forced integration, which Windows is working around.
According to AdDuplex, windows analytics company, 22% of computers running 1809 recently, which is only a 3% decrease from October’s reporting of 25%.