Bingo.
Its way easier to just pop a pill than to have to spend the hours trying to work with your kid to get them the necessary exercise, nutrition and mental activity necessary to prevent (insert your mental illness here).
If I told my mother that I was depressed, she would tell me to go outside until I stopped feeling depressed. Somehow the sunshine, fresh air and my dogs managed to keep my from killing myself.
That's not going to do a thing about severe depression, or a host of other mental illnesses.
My mother was a bit more devious. Anyone caught moping was put to work cleaning the bathroom, diapering babies, mowing lawns, or any one of a list of 2000 household chores. This had a way of clearing the kids out of the house for the rest of the day.