The answer is - a scarcity of natural resources.
This is not a reason at all for poverty in Brazil. Brazil is a country that has abundance of natural resources, oil, gas, timber, water, minerals, you name it. The problem is the way in which this resources are used, not the lack of them. The way of usage of them is suitable for the rich who take the biggest piece of the 'pie', while the poor population barely sees any benefit from them.