You look at some of the most third world places in the world without strong economic security, yet somehow they manage to have babies at a higher rate than Western countries do.
Hell, in many countries in Europe, they basically throw money at anyone having kids and their birthrate has plummeted which would indicate that economics is not only reason.
Would be an interesting experiment to actually pay people to have kids - i.e.: financially reward them in accordance with the costs involved. I suspect, as with an actual liveable UBI, the results would differ radically.
And even if you're not that poor, you get subsidized kids through things like the earned income tax credit and the child tax credit. It's annoying that while some of those support 3+ kids, many "top out" at three and stop increasing.
I've often thought of searching for "sponsorships" for additional children (though we'd probably have them anyway) - not sure I want my son to be named Facebook X AI though ;)
There needs to be a societal change where motherhood is not only respected but celebrated - why we are now in a society where it's looked down upon (not verbally but by actions) could be pondered.
Even within Western countries income is negatively correlated with fertility - those most able to afford kids are having the least number of kids.