Most governments, when building out subways, will choose to build two lines out and get twice the coverage rather than build one local and one express line that serve the same location.
New York was able to avoid this choice starting out, because its CBD and densest areas (Manhattan) are built out in a long, narrow fashion, and you can only thread so many lines through such a narrow space before you start having to make choices between missing transfers and building stops way too close, so the decision was made early on to concentrate tracks for easier transfer facilities.
It's also worth noting that New York's subway was built in an era where buses and streetcars were slow (and in some cases still pulled by horses), so the local lines have stop spacing optimized for walking to a station and the express lines are the actual commuting heavyweights that people transfer to. More modern subways are designed with medium-speed last mile transfers in mind, either via cars that park and ride (BART, DC) or lots of bus transfers (Asian systems.)
Eventually a city becomes too big and belatedly realizes that it needs to have regional express service running through the city, because transferring rail+subway+rail is way too slow. Cities that developed first during the Industrial Revolution can depend on the dense legacy rail networks that were developed during that time (Paris RER, Berlin S-Bahn, London Crossrail) and this mostly consists of building connecting tunnels through the city center with stops at major activity centers.
Those cities that developed during the 20th century mostly don't have dense legacy rail networks, and have to new build after the fact, which can be hard and difficult. Seoul is building a similar network to the above cities, but it's a massively expensive project that they have to build 50-60m underground because no provisions were made to accommodate it before hand. I suppose Beijing and Shanghai will get around to building such a network when they reach a similar level of wealth and can afford it.
New York was able to avoid this choice starting out, because its CBD and densest areas (Manhattan) are built out in a long, narrow fashion, and you can only thread so many lines through such a narrow space before you start having to make choices between missing transfers and building stops way too close, so the decision was made early on to concentrate tracks for easier transfer facilities.
It's also worth noting that New York's subway was built in an era where buses and streetcars were slow (and in some cases still pulled by horses), so the local lines have stop spacing optimized for walking to a station and the express lines are the actual commuting heavyweights that people transfer to. More modern subways are designed with medium-speed last mile transfers in mind, either via cars that park and ride (BART, DC) or lots of bus transfers (Asian systems.)
Eventually a city becomes too big and belatedly realizes that it needs to have regional express service running through the city, because transferring rail+subway+rail is way too slow. Cities that developed first during the Industrial Revolution can depend on the dense legacy rail networks that were developed during that time (Paris RER, Berlin S-Bahn, London Crossrail) and this mostly consists of building connecting tunnels through the city center with stops at major activity centers.
Those cities that developed during the 20th century mostly don't have dense legacy rail networks, and have to new build after the fact, which can be hard and difficult. Seoul is building a similar network to the above cities, but it's a massively expensive project that they have to build 50-60m underground because no provisions were made to accommodate it before hand. I suppose Beijing and Shanghai will get around to building such a network when they reach a similar level of wealth and can afford it.