Volume is everything in manufacturing. Higher volume drives down costs due to scale of economy.
They make the F150 and it's associated components at a rate of almost 500,000 units per year. The Ford Ranger has global sales around 380,000, but less than 50,000 of those are sold in the US.
Assuming Ford distributes manufacturing by global region, their North American-based manufacturing of Ranger components might be only 25% of their North American-based manufacturing of F150 components. Probably even worse than that, considering the F150 likelys shares many components with F250 and F350, which the Ranger does not.