That was just an example - in the book they are positing that most of the things people want to mine on the moon are actually very rare - though there may be a lot across the moon it will nit be easy to mine it because the density is low.
What exactly are they going to mine? I’n “A City On Mars” (Kelly and ZACH Weinersmith) they claim “one estimate suggests it takes 150 tons of regoluth to produce a single gram of helium-3”. How is that useful?
There are lots of claims online about how abundant Helium-3 is on the moon but they all gloss over the specifics.
We have similar treaties for the sea and for Antarctica a d they are generally followed as no country wants to be the one to break them. Not foolproof by any means and it’s pretty likely a rogue character like Trump would push through without thinking about the consequences.