This is precisely why political groups organizing on private companies servers is a bad idea.
Not only do they have direct access to every message anyone in your group has ever sent, they can also, as you can see here, just destroy that history as being accessible to you if they so please.
People like to act like Discord is somehow better, but really, they have just as much incentive to 1. keep an eye on you and 2. remove access if you've become "trouble."
Use privacy respecting services to organize politically (e.g. Matrix).
It's absolutely crystal clear that reddit did this to remove embarrassing history that might have bitten them in the ass in the future. Removing it all in one fell swoop destroys many political groups abilities to organize and destroys any historical evidence of reddit malfeasance that was in direct messages and chats.