I guess this is the reason: https://devblogs.microsoft.com/oldnewthing/20180515-00/?p=98...

> Since its release in Windows XP, Zip folders has not been actively developed. The reason is the usual: Because adding features requires engineering resources, and engineering resources are limited. Furthermore, since the compression and decompression code weren’t written by anybody from Microsoft, there is no expertise in the code base, which means that debugging and making changes is a very difficult undertaking.

“Because adding features requires engineering resources, and engineering resources are limited.“

seems to translate to ‘because we really don’t care’. It’s not as if Microsoft is strapped for cash.

At least they haven't purged it, if this were Google then there would be no ZIP support in newer OS versions.

They even killed ChromeOS ans Chorme updates for a bunch of 3 to 4 year old Chromebooks recently, despite the hardware being fine to run newer ChromeOS.

Why should they? Are they going to make more money if they fix it? Of course not; people aren't basing their usage of Windows on the performance of the built-in unzipper. Advanced users just install a 3rd-party tool, the clueless masses just use the built-in thing and wait and think it's normal. Companies like Microsoft don't care about building the best product they can; they only care about maximizing profits, so the solution that's "good enough" is what they go with. What they have works, poorly, and costs them nothing to maintain, so that's what they stick with.