Alternatively, buying and maintaining a second vehicle (insurance, wear and tear, etc.) is more expensive than just using your current vehicle, which you already need to use a few times a month to haul things in the bed which you'd prefer to do yourself instead of looking for outside help as that takes time.
If there were economically affordable smaller trucks that are likely more fuel efficient than the behemoth trucks - the Ford Maverick hybrid seems to be the start of that trend - then I'm sure you'd see more people purchasing these vehicles used and new.
This is completely ignoring subcultures in the US that roll coal and drive lifted trucks, etc. etc. as they just think that stuff's cool.
That's only really reasonable if you use a truck only a few times a year, honestly. Otherwise it's not reasonable: renting a car isn't extremely easy, often you need the truck for a few days, etc..
But I agree: many people own trucks not because of the utility but because they like trucks.
The rental scene would become different if the incentives were to change. Currently, it is not attractive to rent, so of course the cost and convenience to rent is not optimized as much as it could be by the market.
I can name at least 5 family and friends right off the bat who have large pickup trucks that I guarantee have never used for anything that could not have also been hauled on top of a car with some ties. My neighbor has a 2020 Tundra which I have watched her use to transport her two kids back and forth from the elementary school 1.5 miles away for years now.
It just makes no sense that in the last 20 years, all of a sudden there have been huge increases in the population of the US doing hard, manual work moving heavy workloads such that they can no longer manage with cars that used to work for us in the 1980s and 1990s? I'll go with "it's 90% vanity".
I've switched to a lightweight trailer, pulled by my everyday hatchback sedan.
No fussing with rentals, I can load it up with debris for a trip to the dump while it is detached, and I can fit drywall in it and still have a backseat for car seats.
The trailer cost something like $1000, the tow package $300, plus another $400 to have someone else install it. Probably equivalent to about 30-40 short rentals in price, and far cheaper than a second or larger primary vehicle.
It is also dependent on the cost of fuel. Given that we hardly price any externalities of fuel into the cost of fuel, the current line is probably very far from where it would be otherwise.
They use them for everyday life because energy is so cheap that it does not make sense to inconvenience yourself and use something else.