Some entity (state) has to have the monopoly on violence to enforce laws or there are no enforceable laws.
When there was some kind of micronation-mania some years ago, with multiple mainstream papers mentioning Sealand and that Australian farmer and whatnot, I went to check, and found out that the UN itself is quite dangerous, in fact is why being "UN recognized" as a country is so important (for example why Taiwan would want to be a country officially), the UN navigation laws state that everyone that is a member of the UN has several rights of navigation, and the US for example is one of the main enforcers of these (US warships patrol around the world to ensure "free passage"), but the way those rigths is written, imply that if you are NOT a member of the UN, any member can sink you without any penalty.
Thus the only way to be anywhere on the sea while not being in the UN, is if you are ally of the US (Taiwan), because otherwise you are at risk of being shot at.
I don't think China has yet the navy needed to counterbalance that.
Then the Big Man with the most guns and the heaviest mates becomes the jurisdiction. And you don't get to vote for him.
Because when it boils down to it human beings are just Strategically Shaved Chimps.
So far even attempts are seastading failed due to traditional countries destroying them militarily (one italian attempt for example was just bombed until nothing remained, and an attempt the pacific resulted in nearby countries landing troops on the built islands and kicking people out)