What does it mean that you can't buy enough Songjiang cloth and harvest enough Tang Wei sand?

"I can't buy Songjiang cloth or Tang Wei yarn." This proverb comes from the Ming Dynasty. With the development of China's ancient commodity economy, Songjiang became the center of cotton textile industry in Yuan Dynasty, and by the middle and late Ming Dynasty, the textile industry in Tang Wei and Jiashan around it also developed. There is a proverb that essentially reflects the development of capitalism in China at that time. One, two, three is causality. With the development of capitalism, there is a phenomenon of capital development behind it.