As a wholly owned subsidiary of Microsoft from whom they had just been spun out. I doubt they had anywhere near the capital to staff a AAA production, and even

As a wholly owned subsidiary of Microsoft from whom they had just been spun out. I doubt they had anywhere near the capital to staff a AAA production, and even if they did why not mitigate your downside by working with a publisher? This is standard practice for most large independent developers and for many of the same reasons that people take on investment in the broader business community.