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 antibiotics for a gut infection, a lung infection, and currently a sinus infection. None were improved by antibiotics, but no doctor was willing to do a culture to see what the infection was before prescribing antibiotics because that's the happy path (most infectious are bacterial). I think it might be a systemic fungal infection (I've also had bouts of what I think is thrush), but that possibility is immediately rejected without investigation because 'only immunocompromised people get fungal infections'. Similar for SSRIs. Asked the shrink why SSRIs versus something else - 'got to start somewhere'. Asked them why one SSRI over another, same answer.

Throwing shit at the wall to see what sticks is fine if the cost of being wrong is just the list time of needing to recompile your code. It's 100% not ok when being wrong means fucking up your tendons or making you suicidal.