Why did New York City and Philadelphia become important to who lived outside these cities?
New Jersey, a fairly populous state, is essentially the suburbs of these two cities.
The only state with no network television affiliates is New Jersey, even though it is larger and more populous than most cities that do have some. This is because northern New Jersey is essentially a suburb of New York City and southern New Jersey is a suburb of Philadelphia. Few cities dominate their surrounding areas as much as these two.