In their defense.....A LOT of people are depressed and dealing with it medically. I would guess it might be slightly above the average, but probably not as much as we think.
The reality is that the teaching that works its way into your mind as a JW is that you are never doing enough, even as a JW, you are not guaranteed to not be slaughtered by Jesus, and between the end of the world, and the cognitive dissonance required to be both loving to others on the outside AND be begging God to come and kill everyone in the world.....how could you possibly have a healthy view of the world, yourself, and others?
The branch is obsessed with "keeping the friends busy". They have stated this many times. I don't know if they sincerely think being busy is the cure for this "horrific world we live in", or if the busy part is a tool of control. I suspect its a little bit of both.