What makes you think that great effort is not being put into reducing miscarriages? Miscarriages and stillbirths have been vastly reduced over the last century. You sound as though you think no progress at all has taken place. It turns out that "chromosomal abnormalities are [now] the leading cause of miscarriage, and chromosomal abnormalities are more common in the eggs of older women." [https://www.healthgrades.com/right-care/pregnancy/how-common-is-miscarriage]. After that, the leading causes are life-style choices: smoking, drinking, drugs.
Nature places many hurdles in the way of pregnancies. I'm afraid that "survival of the fittest" applies inside the womb as well as outside. With our current state of technology, advanced as it may be, there is little we can do here. But we are constantly working on it.
After that it is all up to the mother-to-be. Most pregnant women are well aware that they have to take care of themselves during pregnancy.
What more do you think can be done?