I imagine making a modern jet engine is somewhat more challenging than making a ballpoint pen (both endeavours involve making high precision metal parts).
[1] https://www.washingtonpost.com/news/worldviews/wp/2017/01/18...
The numbers given suggested that it cost just over $17 million to import the pen tips to manufacture 38 billion pens. Which puts the cost per tip at $0.00045/piece.
It's not hard to see why manufacturers wouldn't bother creating a process and tooling for that if it already exists.
More importantly, the article put emphasis on the idea that once the government complained about it, something was done quite quickly. Which is completely different story to a military jet engine, which is being researched, funded and developed by government-linked organizations.
I have a hard time believing that China couldn't replicate that technology for 70 years.
"What fool will sell us his secrets?", asked Uncle Joe Stalin. "I will", said Sir Richard Stafford Cripps, CH, FRS.
Or perhaps not; either way, there could have been good reasons - see discussion here[1]
[1]https://www.quora.com/In-the-beginning-of-the-Cold-war-why-d...
China is advancing quickly but they can't make up 200 years of industrial headstart by the west in 20 years.
This is a big deal because the Comac 919 is ready to go but without a powerplant, they're having to turn to Western sources for an engine. The same thing happened with the J-10 project a decade ago and again recently with the J-20. Without a reliable powerplant, you can't build good airplanes and you can't easily reverse engineer a precision turbofan.