>Going 2x faster is obviously a good thing, everything else being equal. Costs can potentially go down as you can run 2x the flights per day. People enjoy flights more.
Unfortunately due to where you can fly supersonic, you're pretty much limited to over water routes. NYC-LON is probably the most financially viable route - but a 3.5-4hr flying time, you can't actually really fly a decent red eye. Ask anyone who has done DEN-NYC. It's a pretty brutal experience.
You leave NYC at midnight, get in at 8:30AM local with a 5 hour time change. You might have gotten an hour of sleep. Sure, some people might pay it, but most would happily leave at 8:30PM and hopefully get 4 hours of sleep.
This was the same problem with Concorde - how do you justify 3-5x the ticket price to arrive less well rested? Who's 4 hours are worth that? It's a pretty small club.
There's a limited amount of daytime flights you can run, but you're going to wind up either running aircraft turns unprofitably to position the plane for your profitable times or having more aircraft than you want sitting on the ground.
Ultimately, it just doesn't really make economic sense. Yes, people value frequency, but they also value money. On NY-LON there's probably 15+ flights a day anyway.
>The difference between a 2.5 hour and 5 hours flight is a lot. A 6 hour and 12 hour flight, a lot.
Unfortunately there's a devil in these details - the plane can't fly a 6 hour supersonic flight. Their rosiest projections are 4,250nm - that puts FCO (Rome) out of reach). That flight is blocked at 8h20m. Of that, especially in NY, 1.5 hours is probably taxiing/climb out/descent. Boom can't do anything about that (except flying out of undesirable airports...)
On shorter flights, that becomes a large percentage of the flying time. I.e. NY-MIA that you could conceivably detour over the water to fly supersonic on, and maybe trim 30 minutes off the total flying time.
Ultimately, the airports where you can fly supersonic to for the majority of the flight are very limited even if you solved the economic challenges.
I still remember hearing the sonic booms from Concorde out on long island - no way frequent supersonic flights get tolerated when they're not well overwater.