Their economy is based on copying things that worked in the U.S. In the 1980s people were worried based on Japan's rate of growth that it was going to overtake

Their economy is based on copying things that worked in the U.S. In the 1980s people were worried based on Japan's rate of growth that it was going to overtake the U.S. Instead they just ran out of things to copy, and the growth completely flattened. At some point you can only grow by doing new things, and for whatever reason Japan has historically been very bad at that.