WHY Japan only has 10 Apple Stores (and probably more on the way)

It would seem that the number of Apple Stores in a given country or geography should correlate with the size of the market. So if the United States with a population of 328 million has 271 Apple Stores, why does Japan, with a population of 126 million and the second-largest economy among democracies worldwide, only have 10 Apple Stores?