I've always believed that at least two out of the following need to be present for a person to be happy in their job:

- money

- learning

- interest

If you have a good salary and you're doing something you like then you're comfortable at present

If you're doing something you like and you're learning a lot then you're working towards your future

If you're learning and earning a lot then you're working towards your future and comfortable(-ish) at present

I think it's good for managers to look at what they should be offering you in this context since they'll know the level of salary you're getting, how much training/development you're getting and how much you enjoy the role. If your staff are only getting one out of three things, then adding one of the others should be pretty easy to do and it removes another reason why they might consider leaving.