It's not just cost of supersonic planes, but sonic booms & how far they travel. So around populated areas it's a no-go. Which means you have to do a good porti

It's not just cost of supersonic planes, but sonic booms & how far they travel. So around populated areas it's a no-go. Which means you have to do a good portion of flight subsonic, and benefit from SS flight over a smaller leg of the yourney. Iirc there were some studies showing that sonic booms were heard by people 100s of km's away. And eg. in Europe: more or less densely populated areas everywhere. So no SS city hopping there. Never mind check-in, waiting on runway & taxying vs. actual flight time. Benefits simply don't outweigh the negatives on most routes. And where they might, too small a market to invest in passing technology / regulatory hurdles.