I'm not sure we'll specifically know the answer there for a while, but I haven't seen much in terms of regional variation that seems especially crazy. Most of the places where it's been especially bad are places you'd expect a virus to spread well - major cities with lots of international travelers and high density. Then you overlay the timelines for when various places took serious measures and you get some logic behind why Chicago is doing better than NYC right now.
There's probably a lot of other factors that feed into it - median age, pollution, weather/temperature, potentially genetic/ethnic factors... Even things like the prevalence and use of public transit. It's a lot harder to get/spread the virus in LA where most people drive private cars to everything than in NYC where a lot of people spend an hour or more every day in crowded subway trains/stations.
Working out exactly what contributed to the real-world outcomes we're seeing is something we'll probably only be able to guess at, but nothing I've seen so far feels inexplicable.
There's probably a lot of other factors that feed into it - median age, pollution, weather/temperature, potentially genetic/ethnic factors... Even things like the prevalence and use of public transit. It's a lot harder to get/spread the virus in LA where most people drive private cars to everything than in NYC where a lot of people spend an hour or more every day in crowded subway trains/stations.
Working out exactly what contributed to the real-world outcomes we're seeing is something we'll probably only be able to guess at, but nothing I've seen so far feels inexplicable.