Transgender question.

Anjelica • Mommy to a beautiful boy 💕
****DISCLAIMER. THIS IS NOT POSTED TO BASH OR BELITTLE TRANS PEOPLE, SO PLEASE DO NOT TAKE OFFENSE TO THIS**** After reading about different types of body issues, a question has been raised in my mind. Someone with body dysmorphia feels like they need to be a certain weight, height, etc., while someone with gender dysphoria feels like they should be the opposite gender. Why is one treated as a mental illness and not the other? Anorexics think that if they get as thin as possible, they'll be happy. What's the difference between them and someone who will only be happy once they change their gender? I am not asking so I can bash trans people, I'm simply asking from a medical standpoint.