i hear you, but i do not fully agree with the analogy...
when i say Russia i mean Russia
when i mean the Soviet Union i say CCCP
when i say UK i mean England, Scotland, Wales etc
when i mean England alone i say England

in the case of 'America' supposed to mean 'USA' that feels like a country 'usurping' the name of a continent.

but yes, i suppose it has just evolved like that for ease of speak and not for pretending to be the continent.