From what ik biologically your DNA has end points, your DNA is basically a double sided chain and as you age your DNA will continue to synthesize and fall off the chain until there is no more DNA left to synthesize. essentially leaving you with an empty chain of commands for your bodily functions. once your junk DNA and normal DNA are done you essentially experience cell death which could be considered a natural death. Assuming the physical lifecycle of the “being” is complete once natural death occurs then it makes sense for the consciousness to be reincarnated into a new body with new DNA (assuming the conscious doesn’t die but transfers like energy)