Most sailors are taught the basics of safety at sea in order to not just keep them alive but to make things easier on the shore-bound lawyers. The more sailors know about keeping safe then the less likely that someone will need to write a check in order to cover some sort of mishap. Knowing what to avoid while at sea helps to keep those checks from being written, even as it helps to save lives. Admittedly those checks will be written at some point, but at least they will be fewer and more far between, and will save lives as well.
Most ship safety is predicated on four basic concepts: The equipment aboard the ship is expensive and dangerous, the ship is in a dangerous environment, mistakes will happen, and the fewer mistakes that happen in the dangerous environment involving the expensive equipment better. The more that the equipment is protected from accidents the fewer accidents that will happen. A lot of precautions are taken care of before the ship even leaves the dock in the form of warning signs placed everywhere and safeties put on the machinery as much as possible, but they are just the beginning.
Those on board must be properly trained on the equipment they will use, as well as any basic emergency equipment. They must also be properly trained in their roles as well as some of the other roles as well; far from sea sometimes the best preparation for an emergency is cross-training. This also means that the captain and the executive officer must also look to train someone else in leadership in case something happens to either, and that person needs to be instructed in emergency procedures as well. The hierarchy aboard ship must also be enforced so that it becomes instinctive and works when it is needed.
A lot of the rules may seem arbitrary but they are based on the idea that rules promote safety. A few rules here and there help to ensure that the equipment will come back to shore in one piece. Better yet, if they are followed then the crew will come back as well. Safety at sea may have been created in cynicism, as an attempt to not write some big checks in response to accidents at sea, but that does not mean that they cannot have some altruistic elements. A few rules may seem onerous, but they can do their job as well as save lives.