Cancer cells are immortal. While normal cells have a senescence trigger. In other words, cell death is programmed. Why would a living organism wish for cell death? A living organism would not want to not live. It doesn't make sense... unless it was rigged.
A common theme in Hollywood movies about clones is that the bio-engineers set up the clones to live a shorter time than humans, for "safety" purposes (usually greed). But Evolution/Nature/Life/whatever would not be interested in "safety". It would be interested in expansion and multiplication, unfettered.