Cost-agnostic business travelers are not a large enough segment of the market for transatlantic flights to justify flying a plane that only seats business class and costs a lot of money. (Boom says they're targeting $5,000 fares between NYC and London [1], and I bet they'll end up being even higher, if/when it gets off the ground.)
Concorde ran a profit until its last flight, actually. It was retired in expectation of how expensive it would get to maintain; it was one of the few planes so analog that it still had a flight engineer seat, when it was retired.
I think the lesson was that business travellers prefer comfort to speed, as business class funds the entirety of transatlantic passenger aviation. There's plenty of business-class-only flights.
I would say it's the exact opposite, after all planes replaced ships and that NY to London leg is significantly more comfortable on a ship. Heck if I could cut my NY-London time in half, I'd take it, even if I had to give up lie-flat seats.
The Concorde was plenty comfortable when it first flew, it's just that it was never replaced. I'm sure boom will offer current business class comforts.
Concorde was very cramped, a longer flight in a first class suite with bed is more appealing, more so now in flight WiFi is a thing so you can work if needed.
