Point of fact, the two worst cities for gun violence are New Orleans and Detroit; Chicago is on the list of bad cities, but at 11.6 murders per 100,000 population, nowhere near the top. Los Angeles is even lower, with a gun homicide rate of 9.2 per 100,000. These cities are also handily beaten by Miami, Atlanta, Washington and Baltimore, among others. They are also beaten by Houston, which comes in at 12.9 gun homicides per 100,000 population.
As for “why does strict gun control not help”, well, actually, in some places it does — like New York City, for example — and in other places, having “strict gun control” right next to places with no gun control, and people having access to that funny technology known as cars, means that “strict gun control” is more an exercise on paper than in reality. Which is not an argument for “no gun control”, it is an argument for a coherent system, consistently applied across the entire country.
Also, the fact that American cities in general have a rate of violence comparable to violent third-world countries rather than other industrialized nations ought to give you a little bit of pause. The whole idea that “a well-armed society is a polite society” is clearly nonsense.