With all the media coverage showing that the female fashion industry is sending out a terrible message of unhealthy body weight and extreme thinness to the public,why are models not shown in proper body weight and size?

fashion models are intended to be living mannequins, showing the design/cut/style of clothing to it's best advantage. curvaceous women tend to distract the observer from the clothes and draw attention to the body beneath. designers want people to remember their clothes, not their models

Because bodies of regular weight and size do not look good in photos, on the runway or in movies, only very skinny bodies look good.

Because most clothing looks better on stick-thin people and these companies are in the business of selling clothing.