'kids today'[1] have quite a lot of representation outside the concentrated city centre - usually city centres have a higher-than-average age. Cool, SF is tiny, compact, and riddled with public transport. Now travel down the coast a bit to greater LA, 20 million people of which have poor access to public transport and live in a very spread out city, limiting the utility of getting around via musclepower. Rinse, repeat anywhere you have spread-out suburbia with poor PT, or outside cities altogether..

[1] article's chosen demographic, though it doesn't really matter