There’s 200+ different viruses that cause the common cold. When you get a sore throat or runny nose you don’t consider those to be the disease, you know there is an underlying cause.
Do you think Depression is similar to that? Do you think it is a symptom of some other disease or diseases?
You shouldn’t compare psychological disorder to organic disease. There is a reason they’re called “disorder” and not “disease”.
Organic disease have a very specific definition and very specifics criteria, so you can actually have a formal diagnosis process. It’s epistemologically impossible to do so for psychological disorder, which have more broad definitions based completely over statistical norms.
P.s. while this is a very important distinction, this doesn’t mean that psychological health is less important or that is not important to seek help and therapy for psychological suffering.