We're a lot more densely populated than we were back then. We also knew a lot less about infectious disease, pollution, etc.. As we learned more about negative externalities of one another's behavior, and as the population grew, it was inevitable that we'd need some rules that went beyond don't steal, don't kill, and don't rape.
Did we manage to live by those 3 simple rules before adding others? If we can't live by 3 simple rules just the hell are we to live by 3 million complicated rules?