Household Waste Segregation

We have two separate garbage bins in our kitchen. I have instructed the Maid properly and she has been doing it correctly. However, no matter how much I try to make my flatmates understand, they are simply adamant. This begs a bigger question, why are so many people so oblivious to the fact that waste is a big problem. I see time and again that people simply don't care which bin they put the garbage into. This is across the country. I remember being taught about this in school and I am sure it is taught in everyone's school. In this post I do not have a complain, rather I want to know why people don't look before putting in the garbage? What are the common reasons?