While I don't directly agree with jrs95, the fact is that the pills just plain don't work a lot of the time. Google the medical term "treatment-resistant depression". The very first link says "
Despite advances in the understanding of the psychopharmacology and biomarkers of major depression and the introduction of several novel classes of antidepressants, only 60%–70% of patients with depression respond to antidepressant therapy." (
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3363299/) Presumably, the odds were worse before.
Consider, too, that that probably doesn't even include those that develop tolerance effects afterward; with that, the numbers likely climb much closer to 50%-50% or worse.