Why is adoption considered as “not the same” as having biological children by some people?

To preface, I’ll say that I don’t intend on having children, so I have no horse in this race. However, when I was younger and considering it in the future, adoption seemed like a no-brainer. Rather than bringing life into the world, you could change the trajectory of someone else’s life. However, I was recently talking to a couple that was infertile that was lamenting that they couldn’t have children. They had known of these fertility issues for a while, but at my suggestion I was told that biological and adoptive children were not allowed all comparable. Why?

The best explanation I can think of is (if I am understanding this right) that after pregnancy women feel a rush of endorphins that help them feel a strong affection towards their child. However, fathers don’t, and still generally play an active role in their children’s upbringing. As my father said to me once, “I don’t love you on any biological basis. I love you because you’re my son, and you’re important to me.” Why can’t adoptive children be seen from this perspective by both parents?