It's an interesting thought, actually. A number of the people who retired at the end of the last Parliament surprised me. I'm not going to mention names because it may be that in some cases health concerns were the real driving force. But they were people who would have been re-elected—they were in essentially secure seats—and they seemed to be enjoying their jobs.
There are people from not just the last Parliament but a number of the previous Parliaments who might be able to shed some light on this. With a bit of judicious searching, I'm sure we could find some people who could explain what the particular stresses were that they faced and caused them to leave. That's a possibility.