Microsoft didn’t kill Rare, and you could argue that they were the victim in the situation ...
In the late 90s, Rare's success caused every major studio and publisher to attempt to poach Rare's talent away from them; and in general, they were highly successful. As this continued, Rare's games were seeing longer and longer delays and (it could be argued) were lower and lower quality; and Nintendo was spening more and more time managing Rare to get products out the door. The Stamper Bros wanted to retire off of the equity in Rare and offered to sell the studio to Nintendo, who didn't believe that it was worth what they were asking and declined.
Microsoft needed a well known first party studio and foolishly bought the controlling interest in Rare from the Stamper Bros. and then Nintendo sold their stake in Rare to Microsoft as well. Since then, Rare has only released a handful of games and very few of them have been particularly good or sold well.
The best analogy to the situation is that Microsoft bought a used sports car and found out it was a Lemon upon delivery
