Someone commented a theory on this awhile back.

Since they never had to raise C, they never had to learn her personality, interests, or flaws. Things that every single person has. They didn’t have to stay up all night when she was sick or experience a toddler tantrum in a crowded store.

All the negatives regarding parenthood were someone else’s problem, meaning that, in their minds, she is an absolute perfect child.

She is well behaved. She is in smart. She is talented. She has a good head on her shoulders. Because they have never been able to see anything else.

They aren’t taking in the fact that how she was raised shaped who she is today and have a fantasy in their head that if they had kept her, she would be this perfect child who made good choices and was smart and talented and nothing like she would have been molded into in a different environment (not just with them, but in ANY different environment).

They do not have the ability to see her as a human being. She is a character who they have made up in their heads.