So I'd like to know why?

First of all the earth is over populated by humans, I believe that is the first problem, there is too little in nature to accommodate for the human population. There is also the difference in involvement in nature between first world and second world countries, where the most developed economies consume resources much faster than the can regenerate. Then there are the developing countries with the rapid population growth which are experiencing poverty and poor living standards. Humans are at a point where they are exploiting nature to meet needs. (Hinrichsen. D, Robey. B)