more developed countries do not have a population growth problem rather their population is steady or decrasing why
In undeveloped countries, birth control methods are too expensive for most people. Also, because of a high infant mortality rate, parents often want several children to make sure some survive to take care of the parents in their old age.
People in developed countries don't have those problems and feel they can only care for one or two children per couple. Also, some people opt not to have kids at all.