This was in large part due to the influence that eunuchs had over the emperor at the time. Many scientists and scholars were banished, if not outright killed, for challenging the orthodoxy of the imperial court. Many of their texts were supposedly burned.
It is quite possible that some ideas migrated from East to West through cities like Venice. In 1987, I attended an exhibit entitled China in Venice; some of the toys that mariners brought back did look similar to some of Da Vinci’s later stuff. Like all great inventors, many of his ideas probably came from a number of sources. To claim they were all Chinese is overly simplistic.
The two words in Chinese, jung guo, actually mean Middle Kingdom, which essentially backs up your second statement.
“The two words in Chinese, jung guo, actually mean Middle Kingdom”
Personally, I think the phrase is better translated, “The Kingdom at the Center of the Universe.” That captures the spirit and intent much better, I think.
Certainly in the “modern” view, there were countries on the map, and China never traded with Egypt, they were too primitive “back then” to actually talk and trade and exchange ideas...which is bunk of course.
Even the Romans had trade relations with India for example, as did the Caliphates with the Far East...
As I recall, the large trading centers in Western China ended up succumbing to desert encroachment.