People, who die without a valid will, die intestate. In this event, the state in which they resided effectively provides a will through the state's intestacy law. This means that the state dictates who will receive the estate owner's property and in what proportion.
While state intestacy laws do attempt to provide for a "fair" distribution of property, the state's "one-size-fits-all" simply cannot reflect the specific wishes of the estate owner in regard to either property distribution or the unique needs of the estate owner's heirs.