Unfortunately this is not a question that can be easily addressed in a single comment on a forum, nor in a blog post. I know my answer sounds like a cop-out, but if you are willing to invest the time and energy, I'd highly recommend reading Ian Morris' magnum opus Why the West Rules -- For Now: The Patterns of History, and What They Reveal About the Future.

This is a good question with a very complicated answer. But to give a short but inaccurate answer: the older a polity becomes the worse it gets at adapting to change due to its internal politics becoming more complicated. We're seeing that in the US right now with the last three very polarizing elections.

There's many reasons. But one of the biggest reasons is probably simply hubris. That is Europe was importing as much technology, philosophy, resources and know how from around the world, leading up to the 18th-19th century. In fact a lot of the philosophers were to some degree familiar with some of the basics of Chinese philosophy, with e.g. David Hume, more than likely reading Chinese Buddhist philosophy (which is why many Buddhist experts tell beginners to read some of Hume's work to understand Buddhist philosophy). The fact that the Chinese did not believe in a god like the Christian God, etc. and yet were an advance civilization did help intellectuals believe that there was an alternative to e.g. scholastic philosophy and to the Christian religion, leading up to the 19th century ideas that there simply was no God (Nietzsche, etc.). It wasn't until around the 19th century when the West began to develop racial theories that they were somehow superior to everyone else, and therefore had nothing to learn from the old world.

The Chinese at some point went around the world during the Ming dynasty, sailing to Africa, etc. Found out that everyone was pretty much uncivilized in terms of technology, etc. and thought there was nothing actually out there. So later on they thought it was simply a waste of government funds to go on such expeditions, especially when everyone seemed to want to reach China instead to conduct in trade rather than the other way around. Therefore the Ming became extremely inward looking, etc. And that carried on into the Qing dynasty. But prior to that in the Song, etc. China was pretty advance. Another issue is that voyages, etc. could not be monetized. Merchants who took risks to explore the world, etc. made 100x more back on their investments, especially after the fall of the Byzantine empire to Ottomans which halted the overland silk road, forcing Europeans to find another route by sea to Asia for items they needed. The Chinese couldn't find such profits at least not in the 14th century.

Obviously this is all very simplistic, and you could easily write 1000s of pages on this topic. But to a large degree today's China is Europe of the past, where they feel they can learn from everywhere, but the West, not so much. Seems as if the two have traded places, where the West is hubristic. Thinking everyone else is pretty much stupid, and uncivilized. Although maybe mentalities of both is starting to shift again.