Because PA time is cheaper to the provider than MD time. Give it a few years and a trip to the doctor's office will mean using a touch screen a-la-mcdonalds to describe your symptoms and then the first-line medication pops out of a drawer. I'm pretty jaded with our (US) healthcare system. As long as you stay on the happy path it's fine, but if you stray from that, good luck. Over the last few years I was given antibi…
Also for SSRIs there's nothing to test, you just try them under medical supervision and if they help they help. There is an experimental DNA test that might be able to narrow down the antidepressant options but unless you're struggling to find one that works for you it's usually not worth bothering.
Medicine is crazy advanced in some specific areas but for the long tail we're not that far from leeches.