After the question I asked in this post, this make sense.
The Bronco's rear window acts as the tailgate lock. So, in order to access the interior bed from the exterior, you have to lower it, no?
Imagine a manual tailgate window... You should need to crawl inside the truck to manually lower the window, then get out to open the tailgate and put your grocery in the back.
The K5 Blazers had a manual crank. I think Dodge Ramchargers did too.
https://www.usa1industries.com/1973-91-fullsize-chevy-gmc-blazer-suburban-tailgate-handle-manual-window.html
Edit: Wait, I think the Ramchargers had an all in one lift door.