I'm curious as to why a CW would propose a guardianship as opposed to working towards an adoption or RU? A guardianship, to me, puts the child(ren) in limbo.
From what I understand, it allows CPS to close the case and it's a LOT less expensive than going to trial for TPR. This leaves the bio parents' their parental rights, limited by the guardian, and the child is out of foster care. Dealing with the parents becomes the guardian's responsibility.
I can see how this may be the best move for an older child who did not want to be adopted, but could not live with the parents. Our children are very young, and we felt they deserved to grow up with parents/parent and I did not want the spector of lawsuits by the mom to regain custody, arguments about what was best for the kids, attempts to limit our authority and ability to protect them, etc. I knew that there would be problems and wasn't interested in living the rest of my life like that.