The OSI is specifically built with a different vision from the FSF.

Free software, shall always be free, with almsource and ideally all derived works.

Open Source wants the code to be spread and for that allows inclusion with commercial software. (i.e. Microsoft was able to take open source TCP/IP stacks from BSD (BSD License) and integrate with Windows 95. That wouldn't have worked with a GPL Free Software implementation. (Even LGPL)

The supporting argument there is: By allowing that Microsoft's implementation was fully compatible to the rest of the world instead of having "bugs" (purposely?) in their own implementation, which would limit interoperability.

The free software argument is that they now took the code and closed it, not giving users a freedom to review (verify) and fix themselves. Which allowed Windows to play in TCP world instead of being an outsider.