Microsoft might not have fully complied with the licence, adding the copyright notice to fix that, won't change a millimeter from what they are doing.
Sure, the MIT is very permissive so it's very easy for Microsoft to correct their repository so that it's in compliance for the future, but they cannot correct the past. (Unless the original authors allow for it.) The MIT license, being so short, does not have a provision about curing infringements.
So Microsoft seems to be ok with the risk of being sued for infringement etc. That's not something you can correct with your personal decisions as author.
The comment above, which I mostly agree with, is that the point of the MIT license to permit anyone, including large corporations, doing this kind of thing. Since this doesn't seem like an outcome the author is happy with, maybe a different license would be better.