US Law often requires power generators to operate separately from distributors. Even when it's the same company, they have to operate as two separate businesses, and it's illegal for them to even mention certain information to each other as it's considered anti-competitive. The purpose is to allow the market to provide competition. This is not specific to NYC.
An Introductory Guide to Electricity Markets regulated by the Federal Energy Regulatory Commission: https://www.ferc.gov/introductory-guide-electricity-markets-...
Deregulation and competition: https://en.wikipedia.org/wiki/Electricity_sector_of_the_Unit...