The short answer is that the wrong people are seeing decreased birth rates.

Religious and poor? To them that equals easily led under educated, and easily controlled. They need this subset of the population in order to continue to extract wealth.

Wealth from the private prison system, wealth from the military industrial complex, wealth from the predominantly labor supported industries that prop up energy, housing, transportation, and other blue collar jobs. To them, more poor babies means more essentially slave or low wage labor.