Whether somebody would have the early stages of their construction project shut down by a flown-in team of military forces from some major nation states (US, Russia, UK) is another question. Or simply blockaded and shut down at places like the ports in Chile, Argentina, Tasmania, mainland Austrlia, New Zealand, South Africa.
You've actually got the same exact problem with the Outer Space Treaty. It only prohibits countries from claiming sovereignty over outer space or any celestial body.
There are 2 non-signatories of the Vienna Convention in Diplomatic Relations.
How would you define a country?
There’s also plenty of “global” treaties that United States is not a party of. Does this make the US a “irrelevant country”?
The US doesn't accede to these treaties because it has a huge economy and military.