> Because he built the city around highways and hence commuting by car, residential areas outside of Manhattan developed into thinly spread suburbs, making it near impossible to create an efficient network of trains. To New York City's credit, they've made a laudable comeback with subways: After all, it's the city you can live without owning cars in the United States.
Your assertions about the suburbs of NYC and the ease of transport into NYC with public transportation are very wrong.
1. There is a massive light rail system that is hugely important to NYC. The Long Island Railroad, Metro North Railroad and NJ Transit Railroads bring hundreds of thousands of people into the core of NYC every single day. You can get directly into midtown Manhattan - which is the most concentrated business district in America - from large parts of NJ, CT, Long Island and Westchester without having to drive. Right now, in the law firm in which I sit in midtown Manhattan, a full 2/3 of the partners commute from CT, NJ and Westchester.
2. A large percentage of people who commute into NYC by car are commuting to the boroughs - not to Manhattan.
3. The residential suburbs outside of Manhattan are comically crowded. We have millions and millions of people living within a 30 square mile radius of NYC. It is absurdly, laughably crowded. Virtually all of Long island is either at city-density or chopped up into 1.4 acre parcels. White Plains and its "suburbs" are super densely packed. Brooklyn - if you want to call it a "suburb" - is the fourth largest city in America. The counties surrounding NYC are all hugely populated: Rockland County (>300k), Westchester County (~1M), Nassau County(>1.3M), Suffolk County (!1.5M), Hudson County (>600k) (NJ), Bergen County (>900k), Fairfield County (~1M) (CT). The city itself is also crazy dense, with >8 million people over 5 counties: New York (~1.6M), Kings (~2.6M), Queens (~2.3M), Bronx (~1.4M) and Richmond (~470k).
So, your "sparsely populated suburbs" contain 6.6M - and that isn't including New Haven County, Essex, Passaic or Union County. I mean, want to talk about a city with sparsely populated suburbs? Look at Boston - or hell, look at Albany. You head out of the city for 20 minutes you are in farmland. It takes hours of driving to get out of NYC and into the bucolic country - unless you happen to come upon some loss-leader farm on long island.
Look, Moses was an autocrat and the decisions he made destroyed a lot of neighborhoods - highways running through residential neighborhoods are very hard to cope with. He was also pretty unapologetically classist and racist in his decision making process. There are many, many good reasons to take issue with Moses the man, his vision and his methods. However, the things you are saying about NY are just not true. The biggest problem we have now is that we need to make at least one more tunnel across the Hudson - probably two more - redo the Port Authority and move Penn Station. I can assure you, however, that our suburbs are about as densely packed as they come in America, and that NYC is, if not the easiest, one of the easiest cities in America to commute into downtown from the suburbs without driving.