The modern world didn’t make having children impossible… it made them optional.
For most of human history, children were economically useful…. working the farm, helping run the household, & caring for parents in old age. Modern life, like the automobile replacing the horse, eliminated much of that necessity.
Once children stopped being economically necessary & became primarily a cost, constraint, & lifestyle choice, birth rates collapsed.
The people still choosing families tend to be those who see children as intrinsically valuable… not as an economic asset or lifestyle accessory, but as a source of love, legacy, & meaning. For them, parenthood is worth the cost & sacrifice because children are the entire point, not the payoff.
You can subsidize the cost of having children, but you can’t subsidize the love & desire to have them.