A license term was not respected; the license allows to use, modify, etc. but not to remove the copyright message or change the copyright to Microsoft.
It's simply ignorance. For example, out of the 600 comments in this post, yours is the only one which was able to clearly articulate what actually happened. And it's all the way at the bottom. It goes to show the headspace most developers are in. This mistake will be repeated by many others until the end of time.
Can someone please explain why?