For starters, the Leaf wasn't a sedan, it was a hatchback. In the US market, hatchbacks have always significantly lagged sedans in sales despite being more practical. The regular Prius has evolved to look sleeker and sportier with each generation, but the boxy hatchback Prius V variant was quickly discontinued after introduction due to poor sales.

US consumer preference seems to weigh aesthetic appeal much more than other markets, even at the cost of function. Some other examples are the rugged boxy SUVs that have an aerodynamic/fuel economy penalty compared to their sleek blob counterparts, or the the coupe SUVs that sacrifice both rear headroom and storage capacity for a "sportier" look.