I think it’s partially that US diplomats get constantly told by Chinese officials about how unstable China is. Everyone in the PLA is obsessed with ancient Chinese stories about ancient Hegemons and they took the lesson that the worst thing a rising power can do is “ask the size of the emperors cauldron” and risk freaking out the hegemon prematurely. I think you’re right that China’s progress is being under counted. But I think that’s exactly what the communist party desires (though only in foreign media, domestic media is a completely different story)