That simply isn’t true. Microsoft documented and shared it’s interfaces to an extent Apple never did. Microsoft’s developer program was the most complete and sophisticated in the computer world. In many ways it still is.

This has always been one of the most bizarre parts of the settlement since the Windows API had not only been published for over a decade and a half, but the method of discloser (MSDN) was well known by the time of the settlement (2002.)

If you go back to the original court case, it turns out that the APIs in question are a very narrow set of protocols used primarily in networking situations for an even narrower set of solutions. While it is possible a third party has since exploited those interfaces, they are not commonly used, nor required, by anyone other developer.

(One claim, where in my opinion the courts blundered, was made by WordPerfect in which they claimed the lack of certain APIs made it impossible to compete with Word. Except Word didn’t use these APIs and WordPerfect never has since. In other words, the APIs in question were a series of obsolete functions that appeared to be far more useful than they actually were. The further irony is that these APIs were documented by several third parties and Microsoft did not act to have that documentation removed from publication.)