It's pretty damn simple actually. Their target audience by and large doesn't use twitter anymore, either.

They're a global issues advocacy organization. "Their target audience" is everyone, or at least it ought to be if they're doing their job right.

Ignoring people of any demographic or political persuasion would be a serious strategic mistake in my opinion.

The current electronic frontier is AI and X is the place where high level AI researchers, developers, influencers and users converse. IDK where else has more of the intellectual discourse on AI. Definitely not the likes of instagram or TikTok. Sure, those platforms are more censored and kid friendly, but I don't think that's really who the EFF should be focusing on as their audience.