It might sound completely mad, but it is actually untrue. In deep-sea tourism, since the sub is carried on the big boat as cargo and only operates in international waters, it is not properly regulated at all. There is literally no government, agency, or maritime organisation that regulates it. The company also ran their Titanic operations through their branch in Bahamas (OceanGate Expeditions), meaning they could also circumvent US laws. So basically what they needed was just for the passengers to sign waivers, which they did. I am pretty sure this now will lead to introduction of more regulations though.