Because the rural folks think that "bad people" live in cities. (Don't ask them too many questions about what makes them bad; it's almost certainly bigotry.)
It has nothing to do with land. It's about the political subdivisions that are states, and how those states have differing concerns (can even be seen in the talks about different commerce and trade concerns when the country was formed).
Cities have no representation at the federal level, so we can leave those out of the question.
Why have states? Why indeed!
One answer: to create a level of governmental organization smaller than the federal one that can act as a set of laboratories for legislative and legal experimentation.
Another answer: to reflect the fact that not all laws and regulations make sense across a diverse range of climate and geography and demographics and economies.
Neither of those answers, however, require states to be considered inviolable sovereign entities, and a lot of us born after 1880 don't think of them that way.
