Have you ever wondered about the design constraints for the Falcon 9 booster? Specifically, why is it so tall and slender?
It turns out that the the Falcon 9 booster is manufactured in California and is transported to launch sites in California and Florida using public highways. Consequently, the booster’s very tall height and slender diameter are dictated by highway constraints, e.g. bridge heights, road widths. The following YouTube video provides an excellent overview.