No nation is restricted from entering any division. Non-US teams can and have entered the "club" divisions before.
The Olympic analogy is off because the Olympics is based on a country vs. country model. Athletes there are not representing private clubs directly. They wear the uniform of their country. Limiting teams by country makes sense in that context.
Worlds, including the "international" divisions, is about competitions between private clubs. The athletes represent Top Gun, Stingrays, etc., - not the United States. They wear the uniforms of their private gyms. Not all of their athletes are even US citizens. We already DO limit private gyms to a single team in each division, exactly like the Olympics limits countries to a single team in each team sport.