Smaller jet aircraft on the same route generally means relatively expensive operating costs: some costs like landing slots and pilots are essentially fixed, whi

Smaller jet aircraft on the same route generally means relatively expensive operating costs: some costs like landing slots and pilots are essentially fixed, whilst others like maintenance, fuel and capital costs don't scale down linearly. The marginal profit on an individual economy class seat might be small, but 100+ of them cover a large portion of the fixed and semi-fixed costs of operating the aircraft, and are relatively easy to fill. Long range business jets which can comfortably accommodate a typical narrowbody business class cabin exist: nobody is certifying them for all-business class scheduled flights because it wouldn't be profitable to do so; likewise the all-premium 32 seat A318 configuration hasn't been adopted anywhere except the NYC/LON route it didn't really have the range for because it wouldn't be profitable elsewhere. Boom's bet is that supersonic changes that.