Yeah, I suspect that there's some sort of unintentional softlock in the game. I spoke with the sailor and the merchant in the town where you get the boat, and sailed the entire length of the ocean north-to-south and east-to-west, and haven't seen any pirate ship. I think that if you do some specific thing out of order, or in a way the developer didn't expect, you can't beat the game, and I have no idea what that might have been.
I even bought the game, too, and feel rather ripped off for it given that it's not actually English-translated as is advertised on the store page and can be softlocked just by playing the game normally.