Notable mention for flat/declining wages since the average cost of raising kids probably doesn't get cheaper as time goes on.
Imaging paying your you and your spouse's student loans, then having two kids and paying their student loans or putting that debt on their shoulders. Much easier before tuition skyrocketed.
Real wages, wages adjusted for inflation, have been flat. So people arent exactly getting poorer (on average) in the US. You're right to point some stuff out, medical care and housing have inflated at disproportionately high rates. Higher education as well, but that's elective. Problem is even in countries, like several European states, that offer state incentives or support or regulation to take the load off parents, birthrates are still low among the educated and well to do natives. In fact I'm pretty sure that's a general trend across the world, the poor and less educated are typically more likely to have kids than people who should be financial more capable of supporting kid, at least up to a certain level.
So economics is probably a weak explanation. Personal freedoms, especially for women, is probably the root cause of low birthrates.
Imaging paying your you and your spouse's student loans, then having two kids and paying their student loans or putting that debt on their shoulders. Much easier before tuition skyrocketed.
Healthcare prices are a consideration too.