Microsoft's issue is that they _can't_ stop OEMs from doing it, or they'll run afoul of antitrust legislation. The Epic v. Google suit (which isn't going well for Google) is based on the argument that Google, as the OS creator, can't impose limits on the software OEMs ship on top of that OS.
If Microsoft can push their own browser so aggressively and make it such a pain to switch to a third-party one they could do other things as well. But they aren't interested clearly, otherwise they wouldn't add bloatware and ads to stock Windows on their own devices.
They're in a weird place with regard to antitrust: they can, to a degree, promote their own software, since it's their own software. But they can't limit what an OEM does because they've already sold their product to OEMs and the business is "complete", as far as US law goes.
By allowing OEMs to do this? Microsoft could stop it if they had any interest in making Windows a more consistent and reasonable experience.
Yes, you can and should reinstall Windows, but you shouldn't have to.