it all started years ago
For those too young to remember, there was NT. It was a cheap-and-cheerful implementation and not built with modular architecture. For efficiency (i.e. to avoid lots of expensive context switches), lots of stuff was built to run in the kernel.
Fast forward a couple of years and hardware is a *lot* faster. Context switches are still costly but the hardware is so much faster that it doesn't matter so much.
Unix-style systems had modularity from the start. Admittedly, sometimes those modules were placed in kernel-space for speed. But as hardware became faster they were moved out to userland - because they were architecturally separate. Sure - this needed some API tweaks etc but the original design supported it.
Unfortunately the legacies of NT mean that can't be done with Windows, absent an entire redesign of the OS and everything that goes with it. That would break essentially every piece of Windows software so Microsoft has decided to not do it.
"Cheap and cheerful". You get what you pay for.