Just a guess, but I imagine this sort of legalese is necessary for them to be able to serve uploaded content to other users without being liable for paying royalties every time someone views/downloads your content. Since Primal also offers media hosting/serving, they would have to consider this in their terms. For instance here is similar wording in the Nostr.build terms of service. Clients like Damus or Nostur, on the other hand, don’t offer their own media storage but rather rely solely on 3rd party hosts.