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.

They should keep copies of all that data, yeah. Being successful in killing closed platforms shouldn't result in any losses for them.

I don’t see how to interpret your comment in a way that doesn’t say “their goal should be encouraging people to be principled, not being being principled themselves.”

You can use a tool of a system you disagree with to raise concerns against that very system. There is no contradiction here, only pragmatism.

GNU tools such as gcc were originally developed using proprietary software until the GNU fabric was dense enough to allow bootstrapping. How else can you achieve anything at all, really?