It's first and foremost a bad DPI independence API design, largely due to a terrible backwards compatibility of an even more terrible legacy stack. It is fixed somewhat in their modern stacks, such as WPF and UWP, but the vast majority of Windows software is not written with these frameworks.
While it is understandable why the legacy baggage is there and cannot be removed, the end result is a big mess, still to this day. Most (but still not all) first party software is OK to good. Third party software (not apps from the store) is a mess, usually either blurry, tiny or downright broken. Windows ecosystem being Windows ecosystem, there are many alternative to almost everything, and some software is improving. But it is still a big mess.
Apple's transition was a lot smoother due to vertical integration, a much smaller software library, more dedicated software developer base (or rather, much more willing to be early adopters of new APIs) and most importantly, a much better designed API without a 20-30 year old baggage.
It should be interesting to see people's reaction to the software, after jumping ship for macOS to Windows on these fantastic displays. I couldn't stand the mess after a week with Windows 10 on my MBP. (But I do use Windows 10 regularly on my desktop, on a "normal" display.)