Bonds for something like are typically secured by revenue. When they issue a revenue bond, they need to have the ability to raise the rates to cover the bond. Current rates only matter if they are too high.

The situation in a place like Flint or Detroit is complicated by the fact that the municipality is depopulating, and they cannot afford the infrastructure built for a few million people that now serves far fewer. In any case, a private entity doesn't have a magical ability to fix this stuff. A private company would just buy the future cash flows at a discount and farm the resource for as long as possible.