First, political turmoil. In ancient times, the management and prosperity of the world were short-lived, and most of the time it was turbulent. Unable to organize education. Even if there is a good system, in a few years, the situation will change or even change the dynasty, and it will go away.

Second, low productivity. In an agricultural society, it is very important to have a full stomach. With a young workforce, it is too late to farm, and most people have no chance to receive formal education.

Third, the hierarchy. Although due to the imperial examination system in the Sui Dynasty, ordinary people were able to study, receive education, participate in science and education, and get ahead. But if you really want to be able to afford reading and have leisure time to read to him, you must come from a good family. The conditions are too bad, and there are some successes, but few. Especially in the later period of the imperial examination system, such as the Ming and Qing Dynasties, all kinds of disadvantages were reflected, and the corruption in the examination hall was serious, which hindered the development of education.

Of course, there are other reasons, so I won't elaborate here for the time being.