The reasons of depression are many. There is still no definitive conclusion in studying depression.
The human brain is not totally within the grasp of science, and the same can be said for depression. Many of the drugs used to treat depression are off target. They come at depression in an indirect way.
There could be more progress if the non-drug related issues were dealt with first. Before taking a lot of drugs and unproven medicines, why not deal with the reasons that make people depressed in the first place: stress, pressure, hopelessness, or a negative environment.