Density is the main factor. In the city there is a competitor every few blocks, so map pack visibility falls off sharply past two or three miles — much faster than in Naperville or Joliet, where the same optimisation reaches considerably further. A contractor working both the city and the collar suburbs is running two different problems with one budget.
The second factor is the freeze cycle. Frost depth rules out footings, post setting and most exterior concrete for a chunk of the winter, which compresses demand for several trades into a shorter run than the national pattern. Storm events add a third variable: a serious wind or hail event produces a spike within days, and that work goes to whoever is already visible, because you cannot build visibility inside the window.