We know that exercise is an effective antidepressant for some people. In pre-modern times people were generally more physically active so I suspect that prevented a lot of depression symptoms.
https://www.health.harvard.edu/mind-and-mood/exercise-is-an-...
Depression is relative. Today on social media, people come away with the false conclusion that they are meant to feel euphoric most of the time.
I don't believe in 'feeling happy', yet every magazine promises me i'll be happy if I just do X. Instagram says if I just follow <blah>, my life will become infinitely better. It's all a joke. I never feel happy, but I am not depressed. And more importantly, I have no interest in constant happiness... how boring. Most days I just feel meh. Sometimes I feel hungry.
It's completely possible that there's something messed up in modern society that causes depression, or in medicine that diagnoses depression and/or prescribes antidepressants, but the null hypothesis would be that before modern times, people were... just depressed. And then more recently that they'd try treating it with cocaine/meth/etc. Or that they'd fail to treat it, and some percentage of those people would commit suicide, and the remainder would never admit that there was anything wrong, both of which mean the outcome you observe wouldn't happen.
Again, this isn't to say there isn't a more interesting answer, just that you have to at least consider the possibility that it's not something about modern society.