You're not looking at the actual history of Microsoft Windows, though. Windows was (and still is, to a large part) built off what was originally a single-user system that would exist ENTIRELY as a standalone unit that was never connected to any other computers. UNIX, on the other hand, started with that kind of functionality in mind.
So, while UNIX has been building off of that original multi-system support, Microsoft had to build up theirs (this becomes especially important with netcode) on top of a system that wasn't made to work like that. To put it simply, Microsoft started with a shoe and tried to make a hat.
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You're not looking at the actual history of Microsoft Windows, though. Windows was (and still is, to a large part) built off what was originally a single-user system that would exist ENTIRELY as a standalone unit that was never connected to any other computers. UNIX, on the other hand, started with that kind of functionality in mind. So, while UNIX has been building off of that original multi-system support, Microsoft had to build up theirs (this becomes especially important with netcode) on top of a system that wasn't made to work like that. To put it simply, Microsoft started with a shoe and tried to make a hat.