Adult adoptions are special. Little kids don't have a lot of say in whether or not they get adopted. But adult adoptions are done where both the adoptor and the adoptee want to have the legal relationship of parent and child. Why would anyone ever want to get a different parent as an adult?
The reasons, of course, vary and are very personal. Sometimes it may be because the adult "child" (adoptee) feels a closer kinship or bond with the adult "parent (adoptor) than with their prior legal parent. Sometimes, the adult "child" (adoptee) was neglected or abused and wants a new legal identity as the legal child of a new parent. Perhaps the adult "child" (adoptee) was adopted as a child and grew up not knowing her biological mother. Then, later in life, she finds her biological, establishes a bond and wants to re-establish the mother-daughter relationship legally.
Typically, child adoptions are done to provide safe, loving homes for children as they grow up. But adult adoptions are usually done more for emotional or spiritual reasons. They are special.
As for the mechanics, they are quite simple because we do not need to get consent of the prior legal parents, and we do not need to present evidence on termination of parental rights. We simply need to get the consent of the adoptor, adoptee, their spouses, and file the petition. We have a brief hearing where both adoptor and adoptee testify that they want the legal change.
What about the prior legal parents? Utah law requires the adoptee to notify his/her prior legal parents after the adult adoption is granted, unless there is good cause not to do so. Sometimes, due to strained relationships, the court will grant the adoptee's request to not be required to notify his/her prior legal parents.
In short, adult adoptions are about finding peace and connection. The law can be a wonderful thing!