It's not about some do, some don't.
Some people care about their ancestry, some don't.
I understand that. Not everyone cares who their grandmother or great grandmother is.
But MANY people care about who their biological parents are. It's not uncommon at all for an adopted child to begin asking questions about their biological parents once they become a certain age. And it goes beyond just wanting to know their names and faces. We inherit personality traits, and even increased vulnerability to certain illnesses from our parents and their family history.
This is why you see requirements listed for education, etc. on here. We are who we come from.
It's not the same as a friendship. This is your parent.