Society puts control and money and thinness on the same pedestal, as well. To be thin is to be in control and to be worthy of attention. The person susceptible to developing anorexia sees all of this very clearly and begins to dislike themselves. Because people with anorexia are generally what is known as all or nothing people, it is hard for them to do anything in between or mediocre. Besides society, there are obviously other factors that can trigger someone susceptible to developing anorexia.
Family is definitely one.
For the majority, notice I did not say ALL but for the majority, the family is not the most stable. Often emotions and problems are kept under cover and are not dealt with in the family of someone with anorexia. The caretakers of the person with anorexia may be perfectionistic themselves. The person may have grown up believing that nothing they do is good enough and that to be worthy of love they must get all A's and nothing less. The starvation may also be a form of control, as well.