I don't feel like the comparison works, because we don't know a clear cure for cancer right now, but loan forgiveness is something we can technically do just fine (it's entirely human made after all)
I don't think you can feel unfairness about something not happening that, to our current knowledge, is not possible. You can feel a bit unfairness if something that might as well have helped you, won't be done for you... For no clear reason.