And so did the Estonia. It sank when the machinery spaces, the larges open spaces on the ship flooded through the many openings in to them. Engine rooms are open at the top via air intakes and exhausts for the engines, generators, air conditioning and other cooling systems.
They can't be closed, once the water reaches them the ship is usually doomed as the volume of the machinery spaces is large enough to overcome the reserve buoyancy in the remaining hull space.
Oceanos flooded through broken sea pipes, it was slow because the ingress was through fairly small diameter openings where the failed sea pipes penetrated the hull. Once it was far enough over and down for the water to get to the large air intake and exhaust openings the sinking rate increased.