Boeing designed the plane to be easily convertible to a freighter because they expected the market for subsonic passenger travel to vanish during its lifetime. Sadly they didn’t get that one right but helps explain why it has done quite well as a freighter. For example the hump allows it to be loaded from the nose.
Kinda the opposite of the Airbus situation where they banked on a mostly single use plane plane that was all about moving a large volume of passengers a long distance and instead smaller planes took over and the plane was of little use beyond passengers.
