Actually, the reason people die is because over time people's genetic codes accrue damage and when damaged cells reproduce the overall performance of the structure (organs, other tissues, etc.) that they are a part of degrades. Eventually the performance of structure can no longer be sustained, resulting in failures in other systems which rely on said structure causing a cascading systems failure culminating in the cessation of life. Also, outside factors can exacerbate this degradation, such as having a piano fall on your head.
Because Of Sin Nature. Adam and Eve was created perfect, but because they rebelled agaibst God sin came into the world. Therefore we became spiritually dead in our sins. Because we chose to walk after the things of the flesh. So everything dies sooner or later. The Good News is we will live forever in the next live. But you have a chose to where you want to spend eternity. You either chose to walk in the ways of God or the ways of self.
God created us with a desire to live forever. (Ecclesiastes 3:11) Our first parents Adam and Eve were created perfect. God purposed that man live forever and that Earth be filled with perfect offspring. (Genesis 1:31; 2:15) But Adam and Eve disobeyed God and in doing so became sinners and no longer could live forever. (Genesis 3:1-6) Why? “The wages sin pays is death.” (Romans 6:23) Adam and Eve now had sin in their genes. They could not produce perfect children any more than a dented mold can produce a perfect object. “Through one man sin entered into the world and death through sin, and thus death spread to all men because they had all sinned.” (Romans 5:12)
Today scientists do not know why humans grow old and die. The Bible, however, explains that we die because of Adam and Eve. Thankfully, God has plans to reverse that! God’s Kingdom will soon do away with sin and death forever. John 17:3 tells us we can enjoy this by taking in knowledge of Jehovah God and his son Jesus. For more scriptures about that Kingdom, see the link below and read along with your Bible!
To make room for those being born. So many people are born that population must be regulated in other ways(via natural disasters,famine,and war). Otherwise the world would be overpopulated and most of us would die
God tells us why we die , read it from your Bible in Genesis chapter 2:16 God told Adam IF ... he disobeyed his command what would happen. after God made him a mate, she disobeyed and In chapter 3, verse 6, Adam disobeyed . Disobeying God is called Sinning. They chose to listen to the wicked spiritual son of God (who used a creatures mouth like a ventriloquist uses a dummy's mouth). instead of being loyal to their loving creator .so instead of living forever as perfect Mankind, God cut them off from him, and, like a electric fan slowly begins to stop after it is disconnected from its power source, Adam & Eve slowly began to die when God removed them from his domain, put them out or his control. This is our history they passed on to us. Gen 3: 16 - 19. And god tells us what death is in Ecclesiastes chapter 9: 5 - 6. God does NOT torment us forever. Our whole person dies! read it in Ezekiel 18:4. it's Our active force called spirit,that returns to God, he restores it to us in a resurrection, if ... he wants us to live in his new heavens or new earth. 2 peter 3:13. RELIGIONS teach torment in a HELL not God's word. He is a GOD of LOVE! Hope this helps you. Jesus tells us that Gods word is truth in John 17:17. And look what it says in Romans chapter 3:3,4.
Expiration occurs because if there was no death, the world would be too overcrowded and everyone would feel horrible. Also no single cell can exist forever, they eventually wear out and are unable to function properly and shut down to prevent endless pain and suffering.