How strange that, of all 35 sovereign nations in the Americas, it's the citizens of the only one to have "America" in its name that call their country America!

It must be an obsession, because it couldn't be the desire to carve five syllables off our nine-syllable mouthful of a legal name.

I mean. I guess we could just call ourselves the Union, for short. Or the States, something like that.

But definitely not all three. That would just be silly.

You're really stretching with the word "obsession", not to mention being inflammatory. It's an abbreviation that happens to lose specificity (as you might expect of an abbreviation - therefore, one must depend on context). In addition, it's a gonna globally common abbreviation. I'm sure the relative commonness of "the US" is higher outside the US, but many people outside the US still call it America too.