Because it’s what you want in life, you want to be happy like them. Please seek help my friend, you sound depressed. Find a counselor, or trusted adult to talk to. Mental health is important and nothing to be ashamed of. Find help, and find hope, because even the darkest nights end and the biggest storms pass. I wish you only the best in life and send love and well wishes. :)
Maybe it’s because you long to be happy like them. You might be jealous. But you will find happiness like that! Talk to someone about it your not alone!
They may want to appear just as the way the bodies look in an advertisement. And if the bodies are unhealthy bodies in the advertisements then that would be a negative reaction to the advertisement.