In the event you are not joking, there are entire industries running on Win32. My industry alone (EDA) is a 100B dollar industry. I'm aware of many others.
There is a lot of Win32 using code out there.
It may even be the case that MS's long-lived flagship products (Office, VS) are not completely free of it.
Everything that makes Windows worth using.
Fwiw my question was not intended to be facetious and it may not be obvious what makes Windows worth using.