Both systems have hospitals in lower Manhattan on the East side. With Saint Vinny's gone Beth Israel has seen a good uptick in business as probably NYU to some extent. NS/LIJ's urgent care center to be located on part of St V's old campus is not going to be enough to handle the growing population of the Far West Side, The Village, Chelesa, East Village and everything south to the Financial District (another growing area).
With NYS's finances in a mess and most NYC hospitals either bleeding red ink or barely breaking even it is survival of the fittest and largest so it makes sense for these two to join forces. CP gains access to NYU's hospital, med school, and maybe university system as well. What will be interesting is that NYU is a magnet hospital (the only other one in NYC is Mount Sinai), and CP not only is not but runs an ADN nursing program