The standard isn't detailed enough to create your own Office implementation. Not even Microsoft Office implements it correctly. Microsoft only created the standard so they could claim they were as open as OpenOffice, to prevent OpenOffice from becoming the standard, to make sure third parties would continue building upon Microsoft Office, and to ensure third party implementations would always be slightly worse.
As leaked emails later showed, even Microsoft employees used the Embrace Extend Extinguish term to describe this project.
I'm not sure why you think the VSCode situation is so different.