Why do adoptive parents have biological kids after they adopt?

I saw a post by an adoptive mom of two. She adopted from foster care but is doing fertility treatments. She got both kids at birth as newborns. She said she wants to feel a strong connection to her kids, wants a kid that shares her genetic traits, and wants a baby who only has one set of parents. She doesn't want to share a child, she wants a child that's all hers. She wants to feel one grow inside her and enjoy motherhood at the beginning.

I've seen adoptive parents do fertility treatments during adoption/fostering and hoping one sticks or doing fertility treatments right after adoption.

I guess for me, when adoptive parents say DNA doesn't matter, why do they have a desire to have biological kids? Isn't their adopted child more than enough? If DNA doesn't matter then why do adoptive parents adopt but still try for or want biological children?

And I'm a former foster youth but see so many infertiles foster to adopt hoping for a newborn, then they get pregnant and kick the kid to the curb or fight reunification.