The manufacturing is really deeply gnarly. Like crazy materials you'd have to reverse engineer the production process for, then reverse engineer how to form the blades so they'll survive insane loads for thousands of hours of operation without failure under extreme temperatures. It's like saying you can make a MacBook chassis because you have a block of aluminum, some hand files, and an Adderall prescription.
Alegedlly they tried, but Airbus didn't fall for it. Search for "Ghost plane Airbus A320 C919" if you want to expand. It is a case of "we have no proof, but we have no doubt": China buys a bunch of A320, one of them disappears and never flies. After some time, a A320 clone C919 appears on their market.
