It's easy to say that as a consumer but you also have to realize there are probably fees, licenses, and other assets they would need to purchase to be able to do that. Since they already had microsoft licenses back then they probably are more comfortable about making the game for xbox. They also had already decided that early in the process so it wouldn't make sense changing the idea a week before release. They probably know the sales and know how the Industry is moving right now better than we do as consumers. I trust these guys enough to be able to know what is the best for the company with its current small dev team and budget.