digitaltrees has it right - those unexpected connections, it turns out, not only form great new business relationships, but are a great source of revenue for local businesses. Trivially, you can think about a group of coworkers walking on a sidewalk and unexpectedly bumping into a cafe or boutique, making a "serendipitous" purchase they weren't otherwise planning to while on their way to a lunch meet. You don't go to a mall for that lunch meet.
Take a look at any place in America that has higher than its surrounding average real estate price, even in less heard of towns like downtown Hunstville, Alabama or Ogden, Utah - what is true about the most consistently profitable, lucrative pieces of real estate? They're home to mixed use development [1] (One case study of this effect - [2]).
It turns out, all those "new" (assumed good bc of their newness) models of urban development, with single use office OR home OR shopping zoning, with square miles on miles of tract housing, with islands of empty parking lots (for that one day a year that they're full) between huge hulking shopping centers, necessitating car use for even the smallest of toilet paper purchases... well, those ideas ran contrary to the organic structure of towns and villages for all of human history.
And while those ideas were so new and fashionable, yes, places like New York suffered. But eventually the novelty wore out. The ticky-tacky houses started looking all the same (that is, depressing - but that's my opinion).
New York didn't die in the '80s and certainly won't because of some subway hiccups. Dense urban models work. For all of human history they worked, in 1950s America, for a brief moment, some people thought they no longer did - but it looks like they still work, and will always work. And tunnels are a great way to keep that valuable mixed use real-estate - for commuters and city dwellers alike.
1 - https://en.wikipedia.org/wiki/Mixed-use_development
2 - https://www.property24.com/articles/mixed-use-developments-b...