New York isn't liberal. It's all about business. And the fact of the matter is, some liberal ideas just happen to coincide with the business environment in NYC. Liberal is the line they sell. The reality is hardcore business.
Liberalism in New York is less about Seattle-style Kum-ba-ya and more about high taxes to support a bureaucracy that Otto Von Bismark would envy.
Bill O'Reilly once referred to Manhattan as the Balkans because everyone has a competing agenda. However, the strongest voices for the liberal agenda reside in NYC. Their views couldn't rule anywhere else in the country, so they gather together in NYC out of a certain herd instinct. NYC offers them safety in numbers.