because alot of the drivers in NYC learned how to drive in 2nd and 3rd World countries, where driving is less regulated. In those countries, the streets are often kind of chaotic and horn honking is how people get down the street without getting killed. Plus, alot of it is cabbies, from those same countries, who are impatient to get down the street and trying get another fare as fast as possible.

I grew up in Philly and only experienced all this horn honking once I moved to Brooklyn in 2006.