Why did Ford create the F-150?
Quick Answer
Ford introduced the F-150 in 1975 as a heavy-half-ton between the F-100 and F-250, partly to sidestep certain emissions rules that applied to lighter trucks. It quickly became the volume seller and eventually replaced the F-100 entirely after 1983.
The F-150 filled a gap and then took over.
The reason
Slotting a heavier half-ton above the F-100 let Ford offer more capability and avoid some emissions requirements that hit the lighter class. Buyers liked the extra capacity, and the F-150 became the standard half-ton.