Not arguing for Microsoft, rather the fact that people put out MIT licenced stuff out there, or similar, arguing how bad GPL happens to be, and then get all up in arms when companies do exactly what the licence allows for.
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.
I don't disagree with the general point but in this case we're looking at what (seems to be) a blatant copyright violation. It would not be any more or less of a violation if the infringed license had been a more or less permissive one, because the license has not been followed.
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 point is that the author would not really be much happier if Microsoft had added a few lines admitting substantial portions of code were taken from Spegel. They probably will do this, but I doubt he will be satisfied with the result either way.
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.
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.