The presenter argues that the reason that American automakers stopped producing sedans (like the Ford Fusion) is not because people were no longer buying sedans but because the automakers could not meet the Corporate Average Fuel Economy (CAFE) standards. The light truck CAFE standards (for crossover SUVs) are easier for the automakers to meet so they killed sedans, leaving only crossovers.
The automakers that were -- and are -- able to meet the high standards for sedans are ones like Toyota and Honda, long experts at building small, fuel efficient cars (sedans).
So the reason that so few sedans are now available in North America is that the American Three automakers artificially reduced the supply of vehicles available, not because there was no demand for sedans.