Why doesn't Japan accept immigrants?

Among nearly 200 countries and regions in the world, only four or five countries have clear immigration policies: the United States, Canada, Australia and New Zealand. In other countries, immigration is usually strictly restricted. There are so many people in Japan that it is normal not to accept immigrants. However, for middle and high-end talents, they can still obtain Japanese permanent residence status (permanent residence visa). For example, if you have a bachelor's degree or above, are officially employed by Japanese universities or enterprises, and have lived and worked in Japan for more than 10 years, you can obtain permanent residence status. High-end talents such as university professors are possible within five years.