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. This is why the dislike towards themselves and the dieting doesn't stop and continues on to severe extremes. Besides society, there are obviously other factors that can trigger someone susceptible to developing a full-blown case of 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. When this happens it makes it even harder for someone who is battling the disorder to be able to ask for help. Asking for help takes tremendous strength and courage as it is, but when the family of someone who has come forward with their problems just sweeps them under the rug and refuses to acknowledge that they need help, it just makes getting treatment even harder. Along with this, the care takers of the person with anorexia may be perfectionistic themselves, and as a result, 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.