Why do people have to die?

My grandmother died today. I’m just so upset because I can’t understand why people have to die. I know it’s a natural process but my grandmother died at 91, and she was still sharp of mind. Why does god have to take us from the people we love. What is the purpose in life? How do people cope with the loss of their family members when they pass away? I just can’t understand why we are born and then we die.