Foremost is probably that it was easier to access on a truck than a car below the floor, and it was unnecessary to change until 1960. That's my guess.
That is a good point, but the truck body design changed with the 1955 2nd series truck,
but they still kept the same floor pedals as in the 1947-55 1st series trucks.
In 1955 the car body design changed, at that time they also changed the pedals from floor to firewall/dash.
Body design change in the truck did not effect pedal location but it did in the car.
