Lack of an industrial base and native experience in doing so. Once one company does it, the experience gained can spread to other companies via employees moving around and forming suppliers for those same companies. For India it also has the issue of brain drain as any of the people working on India's engines could easily jump ship and move to the UK or the US and get pretty good jobs in our aerospace industries and get paid a whole lot more.
Also China does have it's own engines used in its military aircraft.
Designing very efficient engines that are also cost efficient is the focus of a lot of those big primes in the US/UK/Europe so competing with them may be difficult, however there is currently no one trying to make very efficient _supersonic_ engines. All supersonic engines are destined for military jets which care a lot more about peak performance as the primary design parameter. In other words there is no one operating in the segment Boom is trying to develop an engine and they can hire a lot of people from the rest of the US industry who already have a lot of experience designing engines or people who were trained by said people.
Ironically it may be SpaceX who kills off Boom if they're successful in implementing suborbital long distance passenger travel with Starship, though that's still very much an open question if it's possible. Such travel would, if successful, most likely be way faster and cheaper than supersonic long distance travel because of the reduced losses from drag.
If it happens, it'll have to happen dozens of miles out to sea.
This video is outdated (and a surface ferry like shown would be too slow... probably would have to be some sort of aircraft, or the time on the ferry would make the rocket trip not worth it), but this shows the idea: https://youtu.be/zqE-ultsWt0
Also China does have it's own engines used in its military aircraft.
Designing very efficient engines that are also cost efficient is the focus of a lot of those big primes in the US/UK/Europe so competing with them may be difficult, however there is currently no one trying to make very efficient _supersonic_ engines. All supersonic engines are destined for military jets which care a lot more about peak performance as the primary design parameter. In other words there is no one operating in the segment Boom is trying to develop an engine and they can hire a lot of people from the rest of the US industry who already have a lot of experience designing engines or people who were trained by said people.
Ironically it may be SpaceX who kills off Boom if they're successful in implementing suborbital long distance passenger travel with Starship, though that's still very much an open question if it's possible. Such travel would, if successful, most likely be way faster and cheaper than supersonic long distance travel because of the reduced losses from drag.