Didn't they?
I am not questioning the fact that BSD is a commercial and Microsoft 'friendly' license, and Microsoft and Unix vendors hired many of BSD developers, it's a win-win situation for them.
What is so sinister by saying Microsoft at the time didn't particularly like Linux GPL license and their ex-CEO called it a cancer (their words not mine) since it's not compatible with their commercial endeavours at that particular time. Perhaps you have forgotten or too young to remember the hostility of Microsoft towards Linux with their well documented FUD initiatives [1].
[1] Halloween documents: