The trend to sameness is probably due to two main factors, more comprehensive collision safety laws and the push in many markets for fuel efficiency. The colli

The trend to sameness is probably due to two main factors, more comprehensive collision safety laws and the push in many markets for fuel efficiency. The collision safety regulations appear to have caused side and rear windows to get smaller (probably to improve side impact intrusion protection) and pillars to get wider (rollover protection). Aerodynamic drag is a major contributor to fuel efficiency. To my eye there has been a trend (in Australia at least) to blur the line between sedans and hatchbacks. Sedan boots/trunks are getting taller and more sloped to smooth the transition from the rear window. The rear of hatchbacks have been also getting more sloped. Both are attempts to get a more tear-drop shape without overly compromising utility. After many iterations working within the same industry wide constraints, it is not surprising that designers all optimise their designs to similar shapes and sizes. The same effect can be seen in road bicycles. The UCI imposes limits on wheel size and other physical dimensions on bikes that are allowed to be used in UCI events (pro and amateur racing). Above 30km/hr aerodynamic drag starts to a major effect on the power a cyclist needs to output to maintain speed or accelerate. In recent years bike manufacturers have been wind tunnel tuning their designs more rigorously. This has resulted in the aero road bikes from the major manufacturers converging to almost identical designs. Cycling commentators and journalists have started agitating for relaxation of the UCI rules to try to get some innovation happening again.