Before I give any real read to the other replies. There are A LOT of reasons for depression.
First time I experienced true depression, not just some minute of sadness, it was after I had my son. Postpartum depression, brought on by the fact that I was 20 and up until then had no idea how hard caring for another being was and being stuck in an environment that made me wanna scream, the stress caused low milk production which ultimately resulted in having to stop breastfeeding which made me feel like a failure... it went on for a year or two. Women who go through postpartum are normally stressed, tired, and feeling like a failure for some reason...combine that all with hormones being all over the place and chemicals in the brain it's a prime combination for something to happen. Not because someone left them or anything else.
Took Lexapro (anti-depressant) a friend gave me, made me feel like I had a lobotomy, withdrawals were bad when I came off it.
Second time I had depression (still dealing with it) it was brought on by a combination of things. Again, failed my son. Left him with his father and basically ran away from my problems to try and get "myself" back. Only I ran into other problems that left me unable to sleep, still fight to sleep to this day, short of shooting me in the ass with a tranq. gun sleep is hard to come by. Stress and fear, lack of sleep, feeling I have failed my child not once but more than once, and having choices taken away from me all added up and I hit bottom, then bottom fell out from under me and I fell even further. Not because someone broke up with me, not because my life was not fun...lack of money I may have but I always find a way to do what I wanna do.
Was on an anti-depressant for that too for a while, apparently made me a really nice person and coherent, but it made me feel again as if I had, had a lobotomy. Street drugs help sometimes, as does alcohol, momentary treatments that don't last.
So it's not always because someone breaks up with someone else, or because they lead a boring life or have no fun. There are always ways to have fun, people just gotta get creative. Yes, I agree, people are over-medicated and aren't looking for the root cause (why are they depressed)...but it's not always because of one thing or another, it's a combination of everything happening around them and to them. And yeah, there are some people out there who aren't bi-polar or depressed that get labeled as such because they are stuck in a rut and can't get out... a lot of factors go into making someone depressed, truly depressed, not some week or two of sadness. Losing the love of your life could do that to some though. I don't really know where I am going with all this, but it is not always because of a partner breaking up with you... and to some, that would be kinda offense for you to assume so R.A. (I don't take offense, just FYI...but some people might because it seemed you assumed a lot of it is caused by losing a partner).