But, assuming a woman is choosing to do it freely. her baby is unwanted by her. If she wanted to be a mother she would get pregnant some other way. So the baby is being removed from a mother who doesn't want them.
You’re confusing surrogacy with adoption.
Surrogacy is the commissioning of a baby to be removed from its mother - it is purposefully conceived for this reason.
Not an accidental pregnancy which the mum can’t bring herself to terminate, so it’s better to be born and adopted.