Though it would be great, wikitree must also take into account how other countires are diivided. In Canada, it would be City, County, and Province.
Obviously, in the old days, more people lived in towns and townships than in cities per se. In the colonies, both county and colony boundaries changed over time. As the US developed, county and state boundaries changed. It would be an enormous task to have drop down boxes for all times since 0 A.D. and for all places. Poland ceased to exist at least three times in its history and what is now Poland may not have been Poland in the 14th Century.
It would be awesome, but it would take a lot of work to make it work properly for all wikitreers.