Where I'm from adoption is not really common, most people tend to shy away from it to prevent being judged by the society.

Matters of emotions are always difficult to decipher in the sense that, most parents that withhold information about the biological parents of their adopted child tends to have a reason, apart from fear of losing the child affection. For most children they are always curious about their biological parents and sincerely speaking not all the stories that leads to a child adoption is good, some of their parents might be into drugs, criminals e.t.c imagine such a child embarking on a journey of finding their biological parents, it wouldn't end well.

This is why some parents prefer to protect their adopted child from the harsh reality about how they end up being adopted