I think it is multi-factorial.
In addition to what you have already mentioned there are many medicalised pregnancy & birth practices that are not evidence-based:
The use and increase in ultrasounds during pregnancy.
The rise in C-sections.
The rise in epidurals, pitocin and other drugs during labor.
The rise in inductions, (not letting baby initiate labor) resulting in more premature births.
The rise in antibiotic use in labor (due to Group B Strep screening.)
The rise in vitamin-D deficient Moms (and therefore D-deficient babies.)
All of these interventions are creating stress on Moms & babies that never was a regular part of our birth process until about 50-60 years ago.
ETA: I forgot to mention immediate umbilical cord clamping, which is still standard hospital protocol even though it has been shown to have a negative impact on babies' development.