There's a lot of art in the production of truly high tech engines. See for example China's difficulty creating a single crystal turbine blades for a turbo fan t

There's a lot of art in the production of truly high tech engines. See for example China's difficulty creating a single crystal turbine blades for a turbo fan to use in it's J20 stealth fighter. They can of course use a lesser engine, but the capability of the fighter will be much less than its contemporaries. Boeing is most likely buying access to the this art.