ELI5: How is international shipping from China so cheap?

This is a frequently asked question that sparks widespread curiosity, especially with the rise of platforms like Aliexpress and Temu. The 'ELI5' format indicates a desire for a simplified explanation of a complex global economic and logistical phenomenon. Content breaking down factors like postal subsidies, container shipping efficiency, economies of scale, and global trade agreements would be highly valuable to a vast audience of online shoppers and curious minds.