Part of the reason I loved long flights was the ability to put away the laptop and zone out to a book or movie with some wine before landing, dealing with immigration, hotels, Ubers, and days of frenetic, high stress meetings afterward.
The prospect of trying to optimize how fast we can jump from one business trip to another is uninspiring.
Even where fuel stops somewhere like Hawaii are practical, the disadvantage of the supersonic flight is that its still long enough for you to notice they're a lot less comfortable than the first class seat you could have slept and got a morning's worth of work done in...
Building certain premium flights around it, not necessarily; Singapore Airlines operates a 67-seat business class on a plane from Newark to Singapore that only has business and premium economy. BA operates a 32-seat business-only flight from London City to New York via Shannon. And these are just the subsonic flights.
JAL is one of the bigger investors in this project, so it's not as if there's no interest at all.
BA1 rarely flies full. The ego is right there in the number. It’s a novelty.
SQ hasn’t operated business class only since like 2011. It has 67 business seats and 94 premium economy seats. And still probably loses money.
The one you didn’t mention was Stavenger to Houston which... only flies when oil is flying high. Because it’s not profitable otherwise.
Theoretically speaking, if the seat cost per mile is as low as advertised some airline might want to take some business class seats out and put some premium economy in. What a plane does with seating layouts is its own concern.
Edit: These are 1.5-2hr intrastate flights, though. If I were going nonstop to London every week I would be all there for the supersonic. Actually who am I kidding, I wanna fly supersonic just for its own sake.
I can do that when I'm home. But at home I can also stand up, go for a walk, or go to the restroom without having to wait in line, or go to sleep, etc. In a long flight I can do none of these. I can instead suffer from dry air, I have a hard time sleeping in something that is a bad approximation of a bed, etc, etc. Oh, and don't ask me if my kids enjoy 10-hour flights (of which they have experienced a few, unfortunately). Sometimes it's so stressful for them that their immune system is ravaged, so we spend time with doctors instead of enjoying vacation.
The shorter the flight, the better for me. If I can afford it. But before it's cheap it first has to exist.