This happened in the town where I live many years ago. It turned out that the mother was a teenager in foster care, impregnated by her father. No one knew she was pregnant since she was overweight and wore large clothing. She had given birth at home, put baby in a park across the street and cleaned up. I know the details because a friend of a friend... small town. The pregnancy was missed by the foster family, teachers, friends. It was a dire situation and unfortunately the baby did not survive. The foster family was thoroughly investigated but no fault found.
The only reason I'm telling this is to show there are many people in dire circumstances unable to deal with whatever trauma life has brought to them. Yes, there is help available, but some people are emotionally unable to access it, which is a shame in this day and age.
Luckily the baby in the OP's post has survived, and hopefully a good placement will be found for it.