If that was the case, why would they need an MD? Why not just a certificate in prescribing medications and referring to therapists? Most do nothing else.

There are holistic psychiatrists who focus on nutrition and other strategies. Depression has complex etiology that is not addressed by simply medication management or checking thyroid function. While some have mental health needs that outweigh risks, most people fall below that threshold as the medications are just not effective or as effective as placebo or even time alone. These pills often have little benefit and higher risk. Many drugs commonly prescribed for mental health have a very strong link with dementia as discovered from one of the strongest studies I've seen in a long time.

At the top of doctors paid most often by drug companies are psychiatrists:
Dollars for Docs - ProPublica
This is not in the benefit of people with mental health struggles.

Psychiatry needs an overhaul. The only innovation in effective treatments in decades--yes decades-is ketamine, which is out of reach for most people. Nothing accounts for hormones, allergies, different types of thinking, sleep quality, existing health problems, etc.

I understand what you are saying as it is the status quo ingrained in our culture, and perhaps that represents your individual needs, but the argument you present is extremely narrow and lacking important context about the practices and impact on a larger; in fact, a huge number in the population.

Most importantly, what is missed is brain health. If your brain isn't functioning, your mental health is below par. Brain health is completely unaddressed by psychiatry, the medications prescribed do not treat brain health.

People might be interested in this line of thinking:
The Brain Book by Dr. Datis Kharrazian, DHSc, DC, MS