Having arrived on the island via boats, they have an inherent fear of boats (hence their eagerness to sink boats of immigrants), and as such have no boat-builders or sailors. (They even fear their former leader, as his name sounds like "Tony A-Boat").
As a result they are stranded on their island and will become evolutionary complacent due to a lack of natural predators.
Eventually when they finally come in contact with human beings and foreign animals, they will approach them curiously, only to be hunted to extinction.