They saw how much people liked the pirate stuff in Assassin’s Creed 4 and they thought they could just throw a bunch of money ar making another one.

'Okay, mes amis... now let's rip out the ship boarding, the melee combat, fleet management, island traversal, towns, most of the resource stuff and economy, and the single-player aspect! C'est magnifique!'

So far away from what anyone wanted or expected.