blackblogs / noblogs host websites & provide urls for activist groups and campaigns. While in some cases Lemmy might be a better/equivalent alternative, often times its not.

Lemmy is just not as useful for campaigns and long lived activist groups, because the structure and all not needed features distract and make the user experience worse.

Besides this, both hosters have quite a history of hosting and not deleting radical content such as doxxed nazis and claims of responsiblity for militant actions, which is something many Lemmy instances do not have and some would probably deleted specific content based on their server rules.