"Should a car manufacturer not employ someone who could do a useful job for them, just because that person lives in a big city and uses public transport to get to work?"

Should they not? No. Did/do they? Probably. Most people working at Ford own and drive cars, and they're almost all Fords. My understanding is that this has relaxed a bit over the years, but... working at GM and not driving a GM car was considered a mortal sin years ago.

Source: someone who grew up in metro Detroit.