I'm not sure which dimensions you're talking about, but in terms of bed size the F-150 has been very consistent over the years (although I think Crew Cabs — although they always existed — have become more popular). The Ranger still cannot fit a full sized sheet of plywood flat in the bed.
Quick research: the new Ranger's bed size has only increased 0.9" (width) relative to the 1990 version. Bed length seems to be the same.
Everything except the bed size has grown enormously on modern consumer trucks. Nowadays truck beds look proportionally tiny compared to trucks from 20-30 years ago when the bed made up a much larger percent of the vehicle.
Ford knows their market. Most F-150 buyers aren't looking for a functional truck, they want a comfortable commuter car that looks like a cool truck.
Quick research: the new Ranger's bed size has only increased 0.9" (width) relative to the 1990 version. Bed length seems to be the same.