I read your comment as excluding other professions, either public or private sector. It makes perfect sense as a contractual agreement on commencement of work/career.Also the term retirement is misleading - you can leave with a pension after completing xxx numbers of years service - it is your choice - you are not forced out unless in very specific circumstances. Perhaps a better question is to as why, other than financial, that officers leave after completing their service?
I'm not sure what the 'issue' is?
I retired on a full pension after completing 30 years service. I was 49 years and 8 months old. That's what I planned for when I joined. I could have stayed, but chose not to - the job had had enough out of me in terms of front line operational duties - of which out of 30 years I estimate I did 28.5. (I do still work part time, as is my choice)
I would add that the pension system has now changed, and the benefits are not what they were. It could be argued this is a reason for the turnover of officers, and the graduated nature of the pension reforms not making it financially cost effective to stay?
An observation regarding pensions is that some look at 'what I'm going to get when I'm 68', as opposed to' what do I need now'...