Microsoft sells Windows as secure/securable OS: filesystem permissions must be enforced (of course, FS ACLs are a huge part of the reason why Windows’ files-on-disk UX isn’t the best).
Yes, Microsoft could still buy it and then redistribute it as a power-toy strictly for single-user computers, but why would they do that? There’s no secret-sauce in Everything.exe - a summer intern could recreate it in a couple of weeks. Oh, and don’t forget the support costs from people who didn’t read the README and installed it on a multiuser machine and can now see the very non-Elizabethan-era file names inside innocent little Timmy’s My Documents\Homework\English\Shakespeare\ directory.