>>132855172Because when they lost their empire at the end of WW2, they also lost their natural resources. Japan is a nation starved for natural resources. Its primary industries are small and underdeveloped, so it needed to rely entirely on secondary and tertiary industries, propped up by the infrastructure America paid for them to build. That goes in many direction, naturally, but culture, especially in the form of art and entertainment media, is an ideal tertiary export. Electronics and automotive manufacturing, 2 of Japans largest exports, both require the importation of raw materials from other, more resource rich countries. The cost of buying and importing those goods cuts into the bottom line of exporting the finished product. With culture, there's no resource that you need to import. Production is entirely domestic, which means it's independent and free of trade deals, politics, treaties and external dependencies.
For a country with weak primary industry, domestic cultural exports are absolutely ideal. There are few 1st world countries that are more lacking in primary industry than Japan. Their agriculture is such a mess they end up needing to buy food from China.