I get what you're saying, but open soft- and hardware IS a principle, and using nonfree software themselves would come across as hypocritical, undermining their own message.

The technology is there to make their own website and platforms; I'd argue that the problem isn't that they're not active on the big social media platforms, but that they don't produce media in the first place.

They can chuck videos onto their own website, license it under a free license and allow others to repost them onto social media for exposure, for example.