People dismissing conventionally attractive people with BDD

I am not speaking for myself, but I have seen attractive people who seem to suffer from BDD and its like nobody seems to have any time for them😭 they genuinely think theyre faking their crippling insecurity because anyone with eyes would find them attractive. So they are very rude and horrid when they voice any insecutity

Why do people think this is a mental illness that conventionally attractive people are exempt from? It reminds me of that old animated batman episode where that woman hides her face because she thinks shes hideous but shes actually beautiful. But she cannot see it