London on New York are two of the top finance industry cities in the world. There are few other city pairs that are close enough that Mach 2.2 makes the difference between comfortably being able to pop over for a business meeting and return the same day vs. getting a really long and tiring day, and that has such a large population of people where their salaries are high enough that paying $5k to cut a few hours of a trip is cheaper than hiring more people.
On top of that, unless their planes revolutionise supersonic flights, sonic booms is a major limiting factor - they need city pairs where very little of the flight goes over land that anyone cares about, because otherwise permits becomes a major problem.
On top of that, unless their planes revolutionise supersonic flights, sonic booms is a major limiting factor - they need city pairs where very little of the flight goes over land that anyone cares about, because otherwise permits becomes a major problem.