Yup depression must be a part of the story.
Serveral articles I have read seem to indicate the path is also, in part, due to strong employment laws:
1) employees can't be sacked if they are unsuitable for their job, so end up being given "dead-wood" positions, which have no jub satisfaction, leading to depression
2) employers are reluctant to give CDI's resulting in a boom of interim and CDD's, and associated job insecurity, leading to depression
3) unemployed >50s have been lead to understand that in the job market they are worthless, leading to depression
From what I understand work is just so important in the vision of self-worth that putting people on the work-dump ten or twenty years earlier than necessary (i.e. at retirement) is just bad policy..... especially in view of the pensions bomb which is fast approaching and will force more and more "seniors" to stay in/need to work for far longer.
I just wish there was a "reset" button somewhere :-)