The one tech detail chosen is pretty relevant to the economic (as opposed to style) use-case here.

Being able to carry a 4x8' sheet is the difference between a productive vehicle or not for a significant chunk of the contracting tradesman market.

Sure, lots of users want trucks for other reasons where a short box does fine or a second row of seat is the winning feature regardless of box space, but the logic being applied for a full size bed requirement isn't arbitrary.