Because BMI requires no equipment to measure and can be used to observe, on a large scale, the morbidity or disease related to weight within a population. How do you expect someone to conduct electronic body fat measures via a phone interview, or collect data from 100,000 people. This sort of data can give us ideas of where weight or diet is increasing disease morbidity within a population. It is not for measuring individual health. If a doctor took my BMI and told me to lose weight then that would be a gross lack of ethical conduct on their part. BMI should be a tool used when appropriate, and at this stage it is by far the easiest tool to look at population level weight statistics.

This is more about maintaining the bodies health, through proper balanced intake of a wide variety of nutrients. Eating a well balanced diet which far exceeds the bodies need for energy will still result in increased fat stores.

Well it is winter in Australia, thus the higher spread of the disease. The death rate does not appear to be exploding however. I guess our winter is not comparable to some parts of the world though.

From same source: "Because it is based on what is "expected" or thought normal, a few cases of a very rare disease may be classified as an "epidemic," while many cases of a common disease (such as the common cold) would not."