I could return the question and ask what was the point of going official with the Sails/OPG when there already were 2 other official Corsair factions. Or the Omicroners/OSI.
For one, being official gives you the possibility the alter/expand your NPC factions Roleplay, within certain boundaries (or at least others not being able anymore to force their RP onto you, no matter how much you disagree with it). It'd also gives the possibility to openly recruit on the forums and yes, this is important even with large playercount, new members bring fresh blood, fresh ideas and replace older members who aren't that active anymore.
Third reason is, that for some odd reason, official factions are percieved differently in this community. While unofficial groups are usually dismissed as 'unimpartant', 'insignificant' or 'temporal', official ones hold a different weight entirely.
At least that is what I have experienced in two years of playing here.