It can be other things, too: it can be useful to move shit around, it can be safe relative to the car you pancaked, it can lug your family around, it's the result of poorly thought out regulations. But it is also a vanity purchase. It's not bad as the justifications people would make when they bought Hummers back in the 2000s, but it's closer to that than a sheer calculation of utility and efficiency, which should be obvious because they don't have to be that goddamn big to move things around.
Disclaimer: I drive a Honda Fit. These trucks could turn me into paste. I'm irritated that I have to consider upsizing just to ensure my infant son survives a collision with a vehicle whose driver can't see in front of them. But I confess my car is a vanity statement, too. I bought it because I won't have to go to the shop as often (fingers crossed) and I won't have to buy another car for good long while. But it also has the vibe of being smart and urbane. Americans very much buy their cars based on image.