Because there aren't any worth doing? I honestly can't think of any first-party title that would be valuable on MS' current or next-gen console. To me, anyway.So Sony just posted a $1.2 Bn loss for SCEE alone this year.
And in a 7 page thread I dont think a single person has tabled the idea of "going third party" yet.
Maybe with the exception of GT and mmmaybe Uncharted. They're first party, right?