If, as a company, you find that you have a department that has had 5 of the 18 administrative staff leave in a period of about six months (three of whom left within a six week period of each other) wouldn't you be asking hard questions of the management?
I know of a business where this has happened (see post below) but they are not looking to see if there are problems with the management, but are instead saying that the staff who left are to blame for not being motivated, etc. No one is asking why the staff are not motivated. No one is paying any attention to the admin staff, not even when they are complaining to the Harassment Officer. But of course there is a very good reason for this. The manager who is responsible for these staff started as an admin assistant in HR and is a friend of the HR manager, in fact, the Harassment Officer is also a friend, so one of the admins was asked if she could put up with the bullying rather than making waves.
Personally, I'd be putting the manager through the disciplinary procedures, but I have no influence so my opinion counts for nothing.