Answer:
Because of the number of overweight and underweight people
Explanation:
The peaks appear because there are significant numbers of overweight and underweight people, compared with a relative small number of people with normal, average weight.
In today's society there are two extremes: the overweight and the underweight people, they make up the largest part of the population and this is why weight does not follow a normal distribution any longer, it concentrates in the peak measurements. To follow a normal distribution, the number of people with average weight would have to be predominant in a society, which is not a case today.
