Nintendo owned 50% of the company, while Rare had control of the other 50%, but was looking for a buyer. For a while, they assumed Nintendo would totally buy them up, and Nintendo even extended their timeline for that to happen, but they never went for it. Rare then went out looking for respective buyers. First, they went to Activision, and they had a deal, but it fell through in the last minute. Microsoft came along and made a quick deal to buy up 50% of Rare, as well as ownership of their IPs. Nintendo didn't want to share a studio with a console competitor, so they ended up selling their 50% for a very nice sum, and re-branding Dinosaur Planet as "Star Fox Adventures" late into development to ensure that Microsoft didn't get that game for themselves.