First of all, let me say it's uneven across the country. In some regions and in some areas it's easier than in other areas. You have more problems in the Prairies than you do, for example, in British Columbia; more problems in Ontario than perhaps you do in Quebec. So there are some regional differences.
Part of it is because working conditions and remuneration packages aren't entirely competitive with what else is available to those folks with those skills; part of it is because of the absence of dedicated budgets for professional development and for constant training; part of it is because you've got provincial systems where people need to maintain professional licensing requirements, and they vary, and if folks are being transferred from place to place within the Correctional Service, because it's a federal system, their licences may not transfer with them, and there are different standards of practice. So it's a very complex environment, and it shouldn't be underestimated.
I will say this. It's not for lack of trying. The Correctional Service tries hard to recruit and retrain those people.