How can that be if they all offer extensive lines of small and efficient cars that a good number of people drive? Besides, collusion doesn't seem likely given the amount of foreign competition. The majority of Americans have made it clear that they want bigger autos, at least with the usual gas prices. Sorry if that's corp propaganda.
Separately I've heard emissions laws blamed for large sedans losing to small SUVs and trucks due to double standards, but I doubt it would've made a difference, even though I personally prefer large sedans.