Patrick didnt feel it was a sales failure, Square Enix did. This was widely reported back then.
Im sure it wont sell as well on one platform as it would on multiple but there are obviously numbers we are not privvy to which would be the point where it would tip the scales to make it worth it. I would assume that along with whatever money MS gave Square Enix to make this exclusives, MS will also be paying for all the advertising as well which would probably make it a very attractive offer given that last years game was very well thought of but didnt sell what they hoped (and yes, the sales figures they were hoping for were unrealistic to begin with).
Once again I am not saying any of this is a good thing. Just wondering if these are the reasons why such a deal would be made.