Outdoor dining sucks in most North American cities because you get to eat right next to a bunch of loud, polluting car traffic zooming by a few feet away. Last time I ate outside in Chicago I could reach out and touch an idling minivan. No thank you. New York City keeps their garbage, most of the time, again, within touching or at the very least smelling distance of outdoor eateries. The city is loud because it's overrun with automobile traffic. Who the hell would want to eat in that environment?
Perhaps we could work on making the rest of our cities look and feel like the parks that are usually popular places to bring lunch, since, you know, they're quiet and feel safe.