There are a few reasons that they might put out a non-gaas game even if that was the reason Sony bought them, like not competing with yourself. Also the fact that Halo is still Halo, but Bungie doesn't own Halo anymore, and Marathon is a close enough approximation that they do own. But no, looks like they're pulling a Prey and just thought the name was cool, so they put it on the next idea that came out of their heads.