For starters, many people continue to breed because their government gives assistance that increases with each child. Some young women think it would be "cute" or "fun" to have babies yet don't realize that at 17, 18, 19 years old, not many non-entry level (professional) jobs are going to employ them. And it takes a little more than the average fry-cooks wage to support one person, let alone yourself AND a child.

Another reason is that people believe that their love is enough to support a large family. Which is FALSE.

Then you have people that truly believe that they were given the capability to procreate because God (or whom ever) wants them to have populate the earth with many as many children as possible so as to ensure a legion of followers in heaven.

Many poor people in "third world countries" often don't have access to contraceptives, their religious beliefs prevent the use of them or the lack of basic sex education simply leaves them clueless to when they are fertile.

And then there are your average idiots who are too stupid to wrap it up or pop a pill. Or think that kids are meant to serve as lifelong companions or friends who will take care of them in THEIR old age.