the problem as stated many times before is that the modern windows is still based on this same code. this is why a patch made for win 10 also works on 8, 7, vista and xp usually. same code base so patch fixes the issue present in all those versions.
it also will let those who wish to exploit windows an idea how the code is written. there will be trends and common methods used that will give an understanding on how win 10 works in many ways. knowing how the code is written and basic trends it uses helps a lot into creating exploits. how they harden the code or when they don't bother is VERY VALUABLE info to have when looking to exploit something.
i realize many don't know as much about programming as others but this is really the concern here. folks need to stop thinking each windows version is somehow independent of the others. obviously newer win 10 features are unique but they will still be written using the same trends and common methods used since windows became a thing.
think of how many exploits are out there WITHOUT knowing the source code. MS is in trouble here and i'm sure they are looking into the same things i am saying to see how many trade secrets are now in the wild.