My daughter is adopted from foster care and she was placed with me as a newborn, I picked her up from the hospital a few days after she was born. Her first mom had a terrible addiction with drugs and was in and out of jail as a result of it. She wasn't violent stole and did some shady stuff to support her habit. She had already lost parental rights to another child (who was being parented by the child's father, they had different fathers). She was expected to regain custody of the daughter I adopted, but she relapsed and ended up back in jail so the state terminated her rights to her too when she was 6 months old. I adopted her just after her first birthday. Her father couldn't sign TPR (termination of parental rights) fast enough for me to adopt her. Her grandmother wasn't in a position to take care of her and her aunt was a minor. My girl has an open adoption with her original family. She sees her grandma, aunt and half sister on a regular basis and always has. Her original mom died of an overdose when she was 4 and up until then, she saw her too. She tried to get clean, her addiction was just stronger than she was and she didn't surround herself with the right people to help her. Her friends were all addicts too.
I've fostered about 10 newborns and half of them ended up going home to their mom. Losing custody was what worked for them to get their shiit together.
Prior abuse of other children
Baby testing positive for drugs (all babies are drug tested when born)
Homeless (the mother is or will be homeless and cannot provide a home for the child)
Unfit home (usually cases of violence in the home)
I also had one that the mother willingly put the baby in foster care because she was homeless and working to get back on her feet. It took about a year but she did everything the state wanted and she got her baby back.
I have a teenager right now who was pregnant when she was placed with me and had the baby while she was with me. I have the baby too. Her parents are both in jail and she was with a grandma who couldn't handle/control her so she ended up in foster care. She's had a rough life with a lot of disappointments, with the right help she can parent this baby.
Family of the mother/father are more likely to step up and claim the child if they are a baby or toddler, after that it's pretty luck of the draw.. if they do or not.