Why do the human laws of inheritance fail to ensure the justice?

Verse 11 of Chapter 4:

As regards inheritance, Allah enjoins you concerning your children that: The share of the male shall be twice that of the female. In case the heirs be more than two females, their total share shall be two-thirds of the whole and if there be only one daughter, her share shall be half of the whole. If the deceased has children, each of his parents shall get one-sixth of the whole, but if he be childless and his parents alone are his heirs, the mother shall have one-third of the whole. If the deceased has brothers and sisters also, the mother shall be entitled to one-sixth of the whole. The division of all these shares shall take place only after fulfilling the terms of the will and after the payment of the debt (if any). As regards your parents and your children, you do not know who is more beneficial to you. Allah has apportioned these shares and most surely Allah is All-Knowing, All-Wise.