Because past me is obviously stupid.
That, and I'm particularly curious 'bout Edward Kenway. He's (obviously) a salty-pirate seadog, yet he's also an Assassin? The hell's up with that? It completely goes against the Assassins' purpose and moral code. What's more is that Blackbeard respects 'em, so clearly he ain't just along for the ride with piracy just an excuse to get t' targets or somethin'. He's a full-blown Privateer.
I wouldn't be surprised if Edward's lifestyle was half the reason why.Spoiler Alert!Haytham turned Templar