This isn't for any economic reasons, it's because the elderly in Japan are the biggest voting block and are acting as entrenched line against all leftist power grabs in their country. Giving time for the younger generations to grow up, realise 'these guys that talk of the need for immigration, diversity and equality are retarded, look what it did to their countries!' and join them in voting against it.

They need the elderly gone so there isn't enough time for the younger generations to grow up without making the same voting mistakes that happen in the west.