Advertising companies have yet to catch-up with the times. With as innovative, fresh and new as they like to tout their skills the truth is there are known recipes for advertising success and the idea of deviating from them (in their minds) is essentially ruination. Most if the time it's the company that has hired them that really needs to push them into different routes and new perceptions of thinking. This has scared so many advert agencies that more and more are willing to back out of projects and lose a contract then be seen as "risk takers" by more traditional companies looking to hire them. Example: Dove's "Love Your Body" campaign. If you're familiar with this advert campaign it shows and glorifies women of all heights, weights, color, ethnicity, etc. This was considered a very bold undertaking. Not for Dove but for the advert agency they finally got to agree to put it together. Dove fought for this campaign and many agencies drooling for an account as big as Dove scurried off at the idea of not using classic campaign formulas which certainly didnt include women with stretch marks or women who were less then "perfect".
They photoshop the models to look extra extra thin because, even though society says it's wrong, and even though society knows the dangers of unhealthy body dismorphia, and even though everyone (especially women) call it an affront to women's health...... They do it because women continue to buy those products. That's why. Because it sells. And it will continue until all women everywhere finally put their money where their mouth is and STOP BUYING IT.
Its not really the models fault its the coach who coaches them they tell them they have to be skinny and in the models eyes she wants to listen to them to make money and to be "beautiful" Some models are actually healthy and not photoshopped