The main reason for Japans fall from economic dominence was due to pressure from the US governement years ago, China does not have this same unequal power dynamic to worry about.
Pick your poison, as usual, but Patrick Boyle's "How The Japanese Economic Miracle Led to Lost Decades" suggests the fall was entirely of their (Japan's) own making: https://yewtu.be/watch?v=12ddOpt7Hio