If the US's "extreme market democracy" is to blame for this, it is because our system creates a larger population of poor people who then have less access to good health care than in the other countries you mention.
In the US, our attitudes about the welfare state have led us to create a system in which we allow more of our population to be poor. Poorer women often tend to have worse nutritiion and other health habits while pregnant. This leads to less healthy babies.
During and after pregnancy, poorer women will also have less access to good health care. This makes it harder for them to get good maternity care and good "well baby" care. These factors make it more likely that their babies will die when compared with babies in places like Germany and Sweden.
In our system, we are more willing to allow people to become poor because we believe the poor are poor because of their own failings. We do not want to spend much money to help the poor (either to help them get out of poverty or to provide them with good health care) because we feel that they are less deserving. Our "extreme market democracy," then, helps to cause more people to be poor and that, in turn, leads to greater infant mortality.