How would Microsoft destroy win32 platform?

You’re missing the point entirely. Curated stores existing is one thing, curated stores being the only way to access content is another.

Going back to the original point; there has never really been a mobile phone ecosystem that did not actively prevent another storefront existing. There can be no ‘Steam’ on Android or Apple devices because their terms explicitly prevent it - however Android devices are certainly popular amongst certain groups of people based on their ability to easily install software from outside of the curated ecosystem.