30-35 years ago you had a lot of regular cabs and some extended cab full size trucks. Then when they started adding the 3rd & 4th rear opening doors, extended cab became more popular because it was easier to access that area. Then they added the entire 4th doors and second row seating, and people realized they could easily haul the entire family. But you needed a little more legroom for adults to ride back there. So they got even longer. And that's kind of where we are today - almost all trucks are four full sized doors with comfortable second row.
Sometime around mid 90s Dodge redesigned the "midsize" Dakota and it became popular. Larger than the S10 and Ranger, and you could get a V8. At least in my memory that's when the small trucks started growing in size. Tacoma, Frontier, eventually the S10 was replaced with Colorado - they were all larger than small trucks from the 80s / early 90s. Ford kept making the Ranger but no one wanted to buy a small truck when you could get something with a lot more room. Their sales started to drop and they were only popular with the local work / service companies - Rangers were cheap and got the job done when you needed a truck that would only have one guy in it, and only had to haul small loads of equipment in the back.
I think laws on gas mileage also had a big effect (I'm sure someone here is a lot more of an expert on this than I am). Basically different size vehicles have a different target gas mileage. It's easier to hit that target on full size trucks than compact trucks (or was considered impossible to hit on the small trucks). Now that hybrids are more common - it's possible to hit those new standards. I believe for light duty trucks it has basically doubled from about 20 to 40 mpg (no surprise - that's the mpg value on the maverick)
