Why does my spouse need to sign closing documents if they aren’t on the deed?

The property is used as the family’s principal residence. Many states recognize the concept of homestead rights. In these place, a family’s homestead, their primary residence, may only be encumbered, or sold, with consent of both spouses.
The property was purchased during the marriage. In community property states, a spouse automatically gains an undivided 1/2 interest in any property purchased during the marriage – even if they aren’t on the deed. There are some exceptions to to community property laws – Property purchased before the date of marriage and real estate acquired as an inheritance gift.
The property owner dies without a will. Although many states have abolished this, a few states such as Ohio and Arkansas continue to recognize dower and curtesy rights. In these states, if the property owner dies without a will, their non-titled spouse will inherit an interest in the property for the rest of their life.