The only way for these nations to cover the difference is to borrow money from the banks of the rich nations. But this soon leads to high national debts, and a large portion of the poor nation's budget then goes to pay the interest on the debt rather than being spent on the internal development of the poor nation's roads and infrastructure. As dependency theorists see it, wealthy people in rich nations profit from this arrangement in two ways, by getting cheaper raw materials for the multi-national corporations they own and by making money on the loans their banks make to the poor naitons. The people of the poor nations are the losers in this arrangement. Macionis presentation of the factual situation of poverty in Third World countries goes a long way toward setting you up for accepting modernization theory despite its flaws.
Technology is limited.
Population growth is dramatic. Cultural patterns emphasize tradition. Gender inequality is dramatic. All of these point in one way or another toward the sorts of problems Rostow identifies as support for his modernization theory explanation of global inequality. In the developed nations, the technological development we so highly prize took several hundred years to develop.