Likely "NIH syndrome" [1]

[1] https://en.wikipedia.org/wiki/NIH_syndrome

It is probably a mixture of the following: is it anticompetitive, ongoing support, security. I think it is mainly anticompetitive issue.

Windows has been called many times for bundling software since it hurts other software companies. Which leads to government regulation. It is sad since I think probably the windows solution could be better in some cases with the native support.

Low impact. It's not the sort of thing that drives PM promotions, right? If you look at the Gates era it was all about huge ideas like replacing the fs with a database, unified RPC architectures etc. Small things like a better terminal emulator, improved zip support didn't get a look-in because you can't easily communicate them. They just sort of ambiently sit around until someone notices them and is marginally more satisfied than they were previously.

These days the big ideas have gone away, so the small polish finally gets attention.

US DoJ vs. MS

Keeps all kinds of features that are table stakes in Mac OS and Linux out of Windows b/c it's "anticompetitive" to bundle everything a user would want with an OS.