Privateers weren’t pirates, they were state mercenaries and usually went after opposing state forces (eg. british privateers going after Spanish ships and vice versa).

While this is technically true, in practice there was a great deal of fluidity between the two designations, with many pirates becoming privateers and vice-versa, sometimes swapping multiple times over the course of their careers. Furthermore, the fact that privateers generally targeted civilian shipping the same way pirates did, and for the same essential reason (plunder), they’re generally associated with each other.