There are many times where a spouse may purchase a property in their individual name, such as when property is bought before the marriage, a property is inherited, or only one spouse could qualify for the loan.  Even though only one spouse is listed on the title to the property, a title company will require both spouses to sign the deed at closing.  The reason for this is that the spouse may have a marital interest in the property.  The title company's job is to ensure that clear title passes to the buyer, which would mean that any potential interest held by a spouse is released.  Moreover, the title company is not a court or judge and can not make determinations as to what interests a spouse may have.  Therefore, in order to ensure there are no issues down the road, the title company will always require both spouses to sign the deed (or a mortgage or deed of trust on a purchase with a loan), in order to ensure the buyer gets clear title to the property.  

If you want to learn more about this topic, we've included a few videos below that discuss this concept.