Earlier quoted context omitted.
There's no reason why the old Win32 window and widget foundation couldn't have been lifted on top of a modern rendering architecture though, there was certainly enough time to achieve this. This would also reduce the need for creating entirely new UI frameworks every year (or even better, higher level UI frameworks could be built on top of a modernized but backward compatible Win32 widget foundation instead of doing…
If you listed out all the requirements a modern UI framework needs you would find that the original Win32 UI API’s are not viable. Especially if you want to support more than just C and C++. So much code is required to do things we now take for granted that the resulting patterns became new frameworks.
Win32 is old and unviable because Microsoft hasn't bothered making comprehensive upgrades for it and never laid out a gap-free plan for how to move off it. They could have upgraded it more smoothly but never did.