Comment by dlcarrier

The regulation did exactly what it was designed to do: take the base-model Nissan Versa off the market and prevent any low-cost vehicles from competing in the US market. (Remember when brand-new cars were available for under $10,000? Inflation adjusted, that was still less than $15,000)

Sure, ultrasonic sensors have a better outcome than backup cameras in a cost-benefit analysis (https://www.nhtsa.gov/sites/nhtsa.gov/files/nhtsa-2006-25579...) and allow you to simultaneously look out the windows and get feedback from the sensor, but allowing them would have allowed for the sale of cars too cheap to have infotainment systems, and that was not the goal of the regulators.