Here's a wild thought. The reason we aren't curing cancer is because we aren't stopping the things that cause it.
I have heard that very little evidence of cancer, some but not much, has been found in ancient Egyptian mummies. It seems to be a modern thing, which is hardly surprising, given that we all today have measurable amounts of plastics in our bodies, plus high levels of heavy metals etc. and the ozone layer is depleted among other things. Though I would point out that stopping the causes, and curing are not really the same thing.