Sadly, this would make a rocket too heavy to reach orbit. So they end up being 1.1x stronger than anticipated loads. And it's hard to exactly anticipate loads. Vibration can add to a peak load, and it's notoriously hard to model how much vibration might happen. SpaceX rockets are filled with cryogenic methane at -160C, which causes everything it touches to shrink which creates forces between the parts that get cold and the parts that don't. A rocket-sized tank contracts by inches, but has to be supported by the structure around it. A single support member that doesn't move the right way can cause a fracture. So it's actually a hard problem.