In all aircraft manufactures and engine manufactures or rebuilders there are many non FAA licensed workers assembling and installing parts. And unless a licensed person is there watching every step of the process, they have no way of knowing how well the job was done.
And with all the latest Boeing max 8 stuff, having A&P inspectors there adds little improvement to the quality of the job or jobs performed.
Also I am curious why a licensed technician that does not know a thing pretty much about say the engine being worked on can really have the authority? It is something that does not make sense to me. And brings me back to the you can build planes and use that experience to gain your AP, but have no experience on say a Jet or turbine engine, then said person can be the authority on the guy with years of jet overhaul experience that has no license?