Answer:
Because the southern colonies revolved around agriculture
Explanation: the southern colonies made most of their profit through growing crops like cotton, Tabaco, and sugarcane, making densely populated cities redundant, this is the same reason why there were more slaves in the south, because they had more of a use for them and slaves could work on the plantations, if there was a slave in the north they would most likely do similar jobs to a housemaid.