Newfoundland has a population of a half million.  Japan's main island Honshu, twice the size of Newfoundland, has 102 million people.  And, there's not much difference between the two islands in geography and weather.

There is no benefit to increasing the population.  Japanese are a wealthy people who apparently have enough wealth to send hordes of tourists to any country imaginable in the world.  The standard of living will probably increase if the population declines and remains as educated / productive.  Some people in Japan unfortunately live in closets and that will worsen if the population continues to increase.

In contrast to the west, they wish to keep on piling immigrations no matter the cost and don't care about a decline in living standards or worsening standards.