Yeah, it's financial. Unless you can sell to the top of the top, the 0.2% of Chicago (as the Lagrange towers attempted) the economics don't work. The size of the core doesn't scale with the size of the floorplate, so skinnier buildings are less efficient.
NY and Vancouver also have an advantage with bedrock close to the surface. In Chicago or Miami*, the loads concentrated by a building greater than 600-700 feet tall require drilling caissons to bedrock, which IIRC is about 200' down. This is really, really expensive, so you can only justify it with large efficient floorplates and a strong dose of ego.
*whoops, miami doesn't have bedrock. the strategy there is to sink tons of relatively shallow piles or caissons and link them with a huge mat or pile caps.
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la forme d'une ville change plus vite, hélas! que le coeur d'un mortel...
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