The main factor on overall height, is a stand-up height bedroom above a truck bed. Ground clearance is a different and separate component, but I barely avoid dragging the bumper quite often on average driveways. So I would not want any less.
Americans want trucks with plenty of ground clearance, and trucks have been getting taller over the last decade. Not everyone appreciates that ground clearance, but anyone that works or recreates off the pavement sure does.
Not a dumb question at all, Limey :)