For the same reason regular cars that kill e.g. 1 in 10,000 in accidents (as we know them), are more acceptable than a design that might be far more safe individually, but when in the (far more seldom case) one blows up, it kills everybody in its 2km periphery.

Even if the total death count is the same (or even if its less for the new design), the widespread small scale pattern is more acceptable than sudden mayhem.

For one, you could just not get in a car, and avoid recklessly crossing the street in the first case, and you'll be fine. In the other case, in the off chance of a new-car blowing up, it can destroy your whole 5-10 block periphery. I wouldn't accept that...