If you only talk about privacy on already private platforms, it will become a circlejerk in no time. You need to tell people who have no interest/experience in online privacy about it so you can further the cause. This is similar to why the FSF is on Twitter/X.
You tell them Reddit is not trustworthy and they should move out, of course. I am not denying that. I am saying the r/privacy community should not be dead because Reddit is a popular platform whether you like it or not, and people need to be informed about their right to privacy even on a known hostile platform.