NYC rental vacancy is only a bit over 4% city wide. The national average is closer to 6%. It is very expensive to build in New York, and projects can be scuttled at any time due to angry neighbors or intervention by city council. The EIS process adds a ton of cost to new construction. As a result of this risk banks require high returns in NYC than in most places in order to secure loans. If you take a development loan the rental price for the units is written into the loan.