Before Microsoft added TCP/IP to Windows, there were third party ports of the BSD TCP/IP stack to Windows. The winner ended up being Trumpet Winsock, until Microsoft wisely used the same winsock API for their own implementation and embraced and extinguished.
Those ports would still have occurred even if the BSD TCP/IP stack was GPL'd.
The alternative history here would not have been that Wrumpet Winsock didn't get crushed by MS but that MS used another more proprietary technology to do it. They have done it in many other areas, e.g. DirectX vs. OpenGL. You cannot hope to compete against the platform you build your product on.
IIRC, Microsoft wrapped a good chunk of the BSD code with it's native implementation of the Winsock API (I may be misremembering and the BSD code may have only been in the NT or win32 code - it's been decades and I'm pretty sure the whole stack has been rewritten since).
But if there wasn't a bunch of people pushing various implementations based on a permissive licence, it may not have been clear that the demand was there. Winsock (the API) heavily leveraged BSD sockets in its implementation, too. V1 was for all intents and purposes designed to deal with unifying their BSD implementations that had problematic issues because Windows didn't have a lot of the system calls that UNIX/POSIX did (though POSIX was available later on in NT) and allowing inter compatibility. It's not clear that Peter Tattam would have written Trumpet if the API wasn't already published, which was driven by the BSD code.
Also, Trumpet was not free or open source. It was notoriously pirated and illegally distributed.
Before Microsoft added TCP/IP to Windows, there were third party ports of the BSD TCP/IP stack to Windows. The winner ended up being Trumpet Winsock, until Microsoft wisely used the same winsock API for their own implementation and embraced and extinguished.
Those ports would still have occurred even if the BSD TCP/IP stack was GPL'd.