You could phrase it much more politely, but yes, it is very unusual to see anyone write "USian".
Some people are trying to normalize "American" to mean anyone from North or South America, but the reality is, of course, that 99.9% of the time, American means people from the US.
It’s the United States of Mexico, which everyone shortens to Mexico but for some reason you’re not okay shortening the United States of America to Americans?
Honestly United Statesian is more confusing because that ambiguously could refer to Mexicans.
It really sounds like you’re trying to troll and yeah people generally don’t like it if you intentionally get their nationality wrong.
No, the official name (in English) is the United Mexican States. (In Spanish, its structurally the same as the Spanish name of the USA (Estados Unidos Méxicanos vs. Estados Unidos Americanos, but the English names do not follow the same structure.)
> which everyone shortens to Mexico but for some reason you’re not okay shortening the United States of America to Americans?
People in American States [0] that are not the United States of America have very good reasons to prefer to distinguish the adjective for “belonging to the Americas” for the one for “belonging to the United States of America”.
> Honestly United Statesian is more confusing because that ambiguously could refer to Mexicans.
Yeah, that would be a problem if we also needed to distinguish the adjective referring to association with México-the-country from some supranational uses of México but were already using Estadounidense to make that distinction for different uses of “America”, but…that problem doesn’t exist for México, to start with.
Some people are trying to normalize "American" to mean anyone from North or South America, but the reality is, of course, that 99.9% of the time, American means people from the US.