Gay people have used adoption as a way of preserving their rights. For instance let’s say your S.O. was in the hospital and they will only let “family members” in. Your lover isn’t a wife or husband so your S.O. could be dying and you wouldn’t be able to see him.
But if one of you adopted the other, you would be a son or father (daughter or mother) so you could see them.
It would also work for inheritance(SP?). At one time way back I believed they used to allow a person to differentiate between an illegitimate child and a legitimate one in a will.
This would also make an illegitimate child legitimate. Though that stigman isn’t much today.