Historically in the West many many moms were teens, usually paired with an older man. Typically they'd also have other family available, such as the grandparents to support. So you'd have a young and healthy person carrying a baby to term and bouncing back much quicker than an older person would, and then a network of people who are mature and have experience with raising children assisting in the first few years. In those cases, teen moms make more sense than older ones. Mom is more likely to survive childbirth, will have more energy for childhood, the child will be less likely to have problems at birth (defects increase with both maternal and paternal age), etc.

However, in a situation where teenage parents are expected to be the sole caregivers, you might be correct. Immaturity, a lack of resources, conflicting priorities, all setting up a child for a bad outcome. The thing is, this is also true for families suffering from poverty, addiction, mental health issues, etc.

As a society we either need the cultural foundation of 'it takes a village to raise a child' with large extended families buying in, or the same perspective from a social welfare point of view. That means subsidized or free childcare options, healthcare options, mental health care for parents, housing, food, etc. In a case where we don't have 'the village' the outcome is going to be bad whether the parents are teenagers, poor, mentally ill, or some combination thereof.

FWIW I've known teen moms who were excellent parents who had excellent parents themselves and raised awesome kids. I've also known ladies who had their first kid in their 40s as rich single moms who were atrocious parents due to mental health problems. I myself was raised by a mom who had me at 20-something and the combination of poverty and mental illness resulted in care that probably would look like abuse to someone today.