I think the main reason kids in foster care suffer is that the kids are already old and have been through a traumatic situation that caused them to have to be put into foster care. That trauma plus the transition can leave emotional scars. Another problem is the foster parents cannot fully take in the kid. The kid can be taken away from them by the government and given back to the kid's original parents.

Putting a newborn up for adoption is different, it doesn't have either of those problems. There are 2 million families in the US waiting to adopt a newborn.