for a more complete answer.

The law might presume that the property is owned by the family or heirs, but that presumption is not final until a probate court makes that determination and the appropriate taxes are paid on the inheritance.

This part is typical: if there is a risk that the family or heirs can be prosecuted for hoarding gold (because they had knowledge during the period of illegality), they may be afraid to come forward and stake their claims. This would open the door for the government to seize the contents. This typically happens when people drive across the border in a car loaded with contraband, and everyone in the car says "it's not mine." By disclaiming an ownership interest, they lack legal standing to challenge the seizure. The government makes a lot of money this way by confiscating cash. This is also why seizure actions are typically "in rem" actions - a lawsuit filed against the property itself rather than a specific person.