Because this will be exploited by the poorest underclass women who will have lots and lots of children to milk the taxpayer (and that's fine!), the resulting market-based salary won't at all be huge.
It blows my mind that people think this way. You're going to get a lot of children who are wanted for fiscal benefits, but are unwanted from a maternal benefit. So yes, number goes up, but at what non-fiscal cost?
Children were genuinely profitable. Not anymore so birth rates plummet.
Nobody can seriously reason how they are going to increase the overall quantity of children while at the same time increase quality of these children('s lives). It's a tradeoff.
But there is a brighter side, if the whole society still benefits from being economically, demographically and culturally solvent, that may offset that tradeoff's quality of life decrease for these children. As we all see it's quite crappy to be a Little Emperor until you are 18 and then realize that education debt + real estate prices = 8===э