That seemed to be in the past, at least the distant past, the way things worked.

A smith took his son to his “office.” The kid watched. Then the kid got older, and curious. The father imparted his wisdom onto his child, and eventually, the son took over for his old man.

Hence, a family line in one business.

Or to look at another way, why people still carry the surname of Smith, Miller, Baker, etc.