I think that some of that is fuel efficiency requirements forcing convergence.

The sedan thing weirded me out too -- I mean, when I think of a "car", I think of a sedan -- but as I understand from reading, that related to people wanting larger maximum cargo space in the car, like if they had to shove a piece of furniture or something in it. I'm in the sedan camp -- in the very rare case that I need to move something really large, I'm just gonna U-Haul it. But I can at least understand the concern people have.

The truck and generally-large vehicle thing, I think, related to a combination of:

• The chicken tax. American auto manufacturers have a 25% protective tariff covering the "light truck" class, making it much more profitable for domestic sales.

• Fuel efficiency exemptions granted that class (which I suspect may have something to do with regulations resulting from lobbying from said manufacturers and them having incentives surrounding the above chicken tax).

  https://en.wikipedia.org/wiki/Corporate_average_fuel_economy

  CAFE standards signaled the end of the traditional long station wagon, but Chrysler CEO Lee Iacocca developed the idea of marketing the minivan as a station wagon alternative, while certifying it in the separate truck category to allow compliance with less-strict CAFE standards. Eventually, this same idea led to the promotion of the SUV.[106][107]

  The definitions for cars and trucks are not the same for fuel economy and emission standards. For example, a Chrysler PT Cruiser was defined as a car for emissions purposes and a truck for fuel economy purposes.[2] Under then light truck fuel economy rules, the PT Cruiser had have a lower fuel economy target (28.05 mpg beginning in 2011) than it would if it were classified as a passenger car.

• High American towing requirements. That is, American vehicles have far more restrictive towing requirements than in most other countries -- you need a larger vehicle to legally tow a given load than in many other countries. I suspect that the regulations may also have something to do with American automakers lobbying for protective regulation; it pushes American consumers to buy from that protected class of vehicles.

Long story short -- I think that you can probably chalk a lot of that up to rent-seeking out of Detroit.