[Danieru]

Couple posters have replied and attempted to answer, but the true reason is the concept of adult adoption.

These companies have survived because any time the family had only girls, one of the women would marry and their husband would be adopted. Thus making the husband the eldest man, and keeping the business in the family.

Japan having family businesses is not the factor, all businesses were good family businesses before the invention of the stock company. Instead what doomed most family businesses in the west was the eventual chance of getting unlucky with inheritance.

The general acceptance of adult adoption to continue a family line, kept those businesses in a single family and justified passing the business whole to the "eldest son".