Why Possessive Apostrophe isn’t used in "U.S. interests"?

[Odessa Dawn]

However, if Syria’s civil war spills over into the rest of the Middle East, U.S. interests would be threatened.

​

I checked the following link but I didn’t find what I was looking for.

A Tip for the Possessive Apostrophe


​

 

[billmcd]

However, if Syria’s civil war spills over into the rest of the Middle East, U.S. interests would be threatened.

​

I checked the following link but I didn’t find what I was looking for.

A Tip for the Possessive Apostrophe


​

Because "U.S. interests" can be considered a compound (single) noun.

 

[Raymott]

However, if Syria’s civil war spills over into the rest of the Middle East, U.S. interests would be threatened.

​

I checked the following link but I didn’t find what I was looking for.

A Tip for the Possessive Apostrophe


​

"U.S. interests" can mean "American interests" rather than "America's interests", so an apostrophe would not necessarily be used there anyway.
There's no adjective "United Statean", but if there was, U.S. could just as easily stand for it as U.S.'s.
Similarly, "UK interests" could mean "the UK's interests".
Mostly, I think, it's just too messy to write U.S.'s, so an exception has been made.