"Content" (whether "free" or not), and "copyrights & fair use".
Because the mechanism they use to ensure Free Software stays Free is based on copyrights. That "Intellectual Property Judo" thing, you know: Using the law that could *restrict* something, to make sure it's *not* restricted.
So in order to be able to fight for the "copyability" of Free Software the way they are doing it now, they need to defend the whole copyright *system* as-is. (And, given the purpose they want to use it for, they probably want to do so from a particular "angle": Stressing its *non-*restrictiveness.)
That, I think, is one possible reason why they would want to fight for Fair Use -- which the latest adopted, and even more so the proposed, legislation runs rough-shod over -- quite regardless of whatever software is used to view the content.
i.e: "Even if the content is proprietary, and even if Gerald is only ever going to view it in Micorsoft Media Player which has no technical problems playing it, the legislation that locks it into the distribution media is still Evil in and of itself, because it fuxxors-up the principles of copyright".