When I was a boy (in the UK, 1970s) America was usually abbreviated as "the USA". Now I find that that is quite rare, and I almost always see the abbreviation "the US".
I entirely understand that both were considered valid then and are considered valid now. I'm not saying one has come out of nowhere or that the other has disappeared. I've just observed a change in frequency.
Is that a change you're aware of over there? Is there any particular reason behind it, or is it just the constant organic shifting of language doing its thing?