The Reason Why Are Trucks Getting Bigger

Overall, I think between the article and the comments, we cover a lot of the reasons (plural) and I think it's a combination of many of them.

People want a vehicle that works for every (edge) use case they have, even if they forget that usage only comes around once every third year. The bed has to be big enough for plywood, the cab has to fit six adults comfortably, and so on. SUVs are popular for this reason. And beds are getting left behind because it really is an edge case for most to need a long truck bed, while having family ride in the crew cab is at least kind of common. Not to mention, having a crew cab and then a long bed makes for a truck so long, it's really kind of a pain to maneuver it. (Source: Briefly owned a "smaller" double cab Silverado with a 6' 6" (198 cm) bed and it was already ridiculously long.)

It's amazing truck rental hadn't become a bigger business, while everyone gravitated towards nimble, fuel efficient cars, but there has to be a reason for that not happening, and I don't think it's fuel regulations. Among other things, there's an addiction to convenience. Everyone insists that the vehicle in their driveway covers every possible use, instead of the daily uses only, because there's a 20 minute round trip in having to go pick up a rental vehicle for special cases.

All of this is interesting to me, as GMC will reveal the bigger 2023 Canyon later this morning. (You can look at the 2023 Chevrolet Colorado[0] now for a good preview. And for those unfamiliar, it's a "mid-sized" or smaller line of trucks, like the Toyota Tacoma.) The redesign is basically the Silverado/Sierra from 5 years ago and they've eliminated all but one configuration - crew cab and 5' 2" (157.5 cm) bed. No more regular cab, no "long"/standard box. In the car world, the most popular configuration has the best profit margin, so slowly any variations get eliminated by bean counters until only the very middle of the bell curve is left.

EDIT: Also wanted to add that these smaller trucks are much less popular than the larger versions. One reason is the obsession with specifications and capability and features. A lot of times the price difference between smaller and larger is small when you consider extra payload and towing (that only one in ten buyers actually needs), or that features X, Y and Z are included on the larger model but left out on the smaller. Gas mileage is also shockingly similar between the sizes. But in the end, I think too many people buying trucks look around, see that everyone else has full-size, and justify it for themselves, when almost everyone would've gotten their needs met with the smaller options.

[0] https://www.chevrolet.com/upcoming-vehicles/2023-colorado

Agreed, I have that vehicle and it isn't quite so big as the monster pick-ups. I've had a SportTrac since 2001. The key thing is that is only has a 4.5' bed. It isn't jacked up and without a 6'-8' bed, it is quite maneuverable. I hike and camp and kayak and hunt and and and... The smaller bed is problematic when I do need plywood but it just gets strapped down instead. The big problem with this new Canyon that you mention is the height and width (which is only need to combat the higher center of gravity) and engine box of this monstrosity. People don't need an engine that big for this "mid-sized" truck because they won't be towing that big with it. It is definitely big for big sake. It must be that the profit margin is a LOT higher on a $60K truck than a $35K truck. One new truck that is combatting this a little is the new Ford Maverick. It is the same size as my SportTrac and TOPS OUT at $35K all-in. It is not jacked up or with an oversized engine. It is funny that it is quite smaller than the new Ranger which was always the small truck line.

The reason truck rental isn't much of a thing is the same reason people drive into cities with public transportation: time convenience. You can't go when you want and come back when you want when you are dependent on someone else. They want to "just go" without planning. Like you said, most people never use the truckness of their truck and it is a status/ego thing.