Someone has to plow the neighborhood. Someone has to drive the power washer to the worksite. And so on.
And the farther you live from a city, the more likely that someone is either you or someone who trusts you enough to borrow their truck.
Some people have a good reason to own heavier vehicles for private use, but even in a rural setting, those are few and far between. There are many more good reasons to own such vehicles for a trades person or a farmer. Commercial use of those vehicles is completely justified.
Maybe it is an American thing I don't get, but there seems to be a confusion between private lives and the work people are doing? Someone does have to cart the tools and materials to the worksite, but that person should be using a work vehicle. There doesn't seem to be a need for that person to own their own truck and pay for their own gas?
But sure, I take your point, there are legitimate, "ordinary" needs to pull a lot of weight sometimes. The question is whether the frequency of these really justifies this sort vehicle being someone's daily driver.
There are many pull-along vehicles ("campers", "trailers") that offer precisely the same space and features as any particular fifth wheel, but connect to a regular ball hitch instead.
At least that is how I've learned the meaning of this term.