Well if you think about it, the show focuses on humans, but only Federation humans. If you go to the Romulan or Klingon section, there'd prolly be a bunch of ships.
Except most of the ships were only mentioned indirectly and the main ships are usually not in the vicinity of earth, so non-human ships should be seen more often.
united states ship united space ship oUr viewerS are moronS and can't accept a ship that doesn't have the registry USS, even though quite a number of them aren't from America in the first place