Why doesn't Japan accept immigrants?

As the country with the largest population density in the world, Japan has been unable to afford immigrants. On the contrary, the government encourages its own people to emigrate, and both Hawaii and Brazil have Japanese communities.

If you can work in Japan, get married and accept Japanese permanent residents, but you can't join the nationality, it will limit the increase of Japanese population.

Accepting immigrants has advantages and disadvantages. Japan belongs to a country that needs young people, and its population is excessively aging. Most people who can immigrate to developed countries are between the ages of 35 and 45. Countries like Canada and Australia need such people most. They have money, mature technology and stable families. But Japan is the country that needs middle-aged and elderly people the least, which will only increase the burden on the government.