Most of the pictures of tenements were on the Lower East Side. The demographic changed there drastically in the 60s. The waterfront changed around that same time also, due to the loss of shipping. The fight over containerization vs bulk cargo spelled the deathknell for Manhattan as a major cargo port. The advent of commercial jet travel killed the passenger ship business. The flight to suburbia with the attendant rise in auto ownership killed the ferries. People took the bridges and tunnels to cross the East and Hudson rivers.
As to what you saw on TV and in the movies, always remember, Hollywood is the land of make believe.
Thanks, that seems to answer my question, although the 1960’s produced the disasters we have today I don’t think they are responsible for the initial transformation which was long term and already under way.
It seems that NYC isn’t really a place for ordinary working families but that economic changes post-Second World War, exacerbated by social “reforms”, would have been behind the decline.