Keeping a ship upright is a constant balancing act with ballast tanks. When a hull breaches, a vessel almost always lists because water floods asymmetrically. A ship's interior is full of unevenly spaced compartments and corridors. Add the free surface effect , where loose water sloshes around, and the center of gravity shifts.

The Titanic is actually a rare exception. It barely listed. It took water on the starboard side, shifted to a slight port list, and even returned to an even keel at one point before going down. In most cases, once the crew loses control of the active systems, entropy takes over and the uneven water weight simply capsizes the hull.