i think those stats show the opposite. They had higher fertility rate when things were worse, but women mostly didnt have a choice. Now they're better but still bad, and women do have a choice - so they are choosing not to, judging by the collapsed birth rate.
That's still a high fertility rate for a country with stats like this: https://www.globalhungerindex.org/bangladesh.html
> 25.1% of children under five are stunted, 10.7% of children under five are wasted
And the country had even higher fertility rates when it had higher frequency of famines, and much higher rates of hunger and malnourishment.
The point i was making however, is that parents don't truly - at a deeper level - consider the quality of life they are subjecting their child to.
Natural selection doesn't maximize for quality of life (it doesn't care for it), it selects for procreation and survival.