Why is Japan not considered one of the gunpowder Empires

The Period of the Gunpowder Empires also known as the Era of the Islamic Gunpowders refers to the epoch of the Ottoman, Safavid and Mughal empires from the 16th century to the 18th century. The three empires were among the strongest and most stable economies of the early modern period, leading to commercial expansion and greater patronage of culture, while their political and legal institutions were consolidated with an increasing degree of centralisation. They underwent a significant increase in per capita income and population and a sustained pace of technological innovation. The empires were centralised from the Eastern Europe and North Africa in the west to between today's modern Bangladesh and Myanmar in the east.