JFK-LHR has all those WALL Street Investment bankers, Media types, Park Ave. types, and Jet Set flying the route. Miami is not a financial center on the level of BOS, ORD or JFK is so MIA-LHR is not a profitable because a pool of high spending business types doesn't exist in Florida. The CONCORDE flies to JFK because there is a deep enough pool of high spenders in New York or traveling to NYC. Miami will be an intenational city of the level New York, London, or Hong Kong are. JFK-LHR is the biggest route for British Airways, Virgin, and AA in their Atlantic portfolios. Miami equivalent is MIA to Sao Paulo.