The answer is "love", you robots.
No, lack of contraception is not the issue here either. What, do you think that because you have low monetary gain you are perpetually unhappy and would not want to have children? That all procreation coming the poorest are mistakes and accidents?
That's quite a nice bubble there. Sorry to burst it.
If two people love each other enough, they might want to have a child. Yes, even if the future is unclear. Yes, even if it means selling the car, taking the public transportation and working over time and having multiple jobs. Whether the situation is permanent or temporary is not even an issue here.
Plus. Having a marriage and children, and getting all financial assistance needed to achieve that is a human right.
The US has signed the treaty enshrining that principle into law ... case closed.
Accidents being the exception, having a child is a huge decision. Especially if you are quite poor.
I have no idea what your personal experience of life is, nor your background. But you seem to have some skewed vision of life if you believe that "these people" shouldn't "produce children" as if the poor were not even humans.
Poor people have children for the same reasons rich people do. The only exception being that there are less gifts at christmas.
Are they robots for practicing family planning? Do they not familiar with "love"?
Because "love" totally makes condoms not work.