In order for a ship to break up while sinking, every ship would need to be modeled in pieces in the first place and equipped with complex dynamics to make each piece behave realistically when separated and stay together when not sinking.
This would require a huge redesign effort and place a much higher burden on the system. Because sinking is such a minor occurrence when the simulator is used as it is intended, and as the majority of customers want to use it, it is unlikely that such effort would be justified to satisfy the lusts of a lunatic fringe.
