>Even back in their prime, I saw many more F-150s than Rangers.
I think you're misremembering. The streets were flooded with Rangers and S10s back in the day. Full sized pickups have been the most popular class of vehicle for decades but that number is grossly inflated by the amount that are bought as fleet vehicles or work vehicles.
It doesn't matter why the number is inflated. If full sized trucks are most popular, then that's what you'll see more of. In any case, there are many people for whom a full-size pickup is their daily driver and not used for work. HN is constantly complaining about it, just not today apparently.
Looking at the Ranger, it sold 5.6M units between 1985-2005, its highest selling years.
F series Fords definitely outsold it, but is also a larger product line.