That is kind of the point - why is the dad who wields a pencil going to have to leave his children in a worse position than a dad who wielded a hammer.
Let's say "a dad who wielded a hammer" is a dad who builds and sells furniture.
Are his children entitled to every piece of furniture this "dad who wielded a hammer" ever built? As it was already mentioned "The dad who wields a pencil" can just as easily buy a house and leave it to his children.
The problem with immaterial things is that they can be trivially copied. In this sense copyright law is more akin to patents: you get protection and possiblity to profit off of your immaterial work.