I said above: because Microsoft (or rather, their Xbox division) owns a bunch of gaming studios, and acts as their publisher. And one of the roles of a publisher, is to get the games the publisher has rights to, ported to more systems, to get them into the hands of more people, to make more money.

Make no mistake: any time an Xbox title isn’t explicitly chosen to be a “console exclusive” for marketing purposes, Microsoft would love nothing more than to port it to every system imaginable. Look at what they did with Minecraft.