Summary: by a senior member of staff...
Here is an interview of a senior member of staff, who was part of a committee discussing PostDocs. He starts an interesting discussion, here is what I kept:
Postdocs are invisible. Many departments don't even know how many they have. There is no responsible person for them, at best it is the same person that worries about PhD students.
Most postdocs leave academia. When they are prepared for alternative careers, it is an afterthought, but in most cases they are on their alternative career by being in academia! The training they receive has no goals.
Most have ended up there because they thought it is an inevitable/default part of their career. No alternatives are shown by universities.
One solution is to raise salaries, and hire less so they are taken better care of.
Seems like a bubble that will at some point burst.
More discussion at quora.