Alright, so first you didn't read the post. It's about two trucks with the same bed size. However, one of the trucks is pointlessly large, to the point that it's actually harder to use it to haul things since the bed height is so much higher. A truck with a lower bed is easier to load.

Second, the vast majority of trucks are never used for anything a sedan can't do. If your bed liner doesn't have any scratches, you could have saved a lot of money and CO2 with a sedan. Hell, if you do need the cargo capacity a van (including a mini-van) can haul more cargo than a truck. A truck's advantage is that it can carry oversized loads, not a lot of cargo.

Third, if you do occasionally need a truck or other cargo carrying vehicle, it's probably cheaper to rent one the few times you need it. The amount of extra you're paying in gas and everything else will almost certainly outpace the price of a rental a few times a year it's needed.

Obviously there's still some use cases for a truck. The smaller one will be better though, and 99.9999% of US truck owners don't fit this group.