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.
F series Fords definitely outsold it, but is also a larger product line.
No, it is because emissions regulations. A small truck can’t be built on our emissions policies, not that there isn’t a market for one.