Because forgiveness is like this: a room can be dank because you have closed the windows, you've closed the curtains. But the sun is shining outside, and the air is fresh outside. In order to get that fresh air, you have to get up and open the window and draw the curtains apart.
Death is nature's way of making things continually interesting. Death is the possibility of change. Every individual gets its allotted lifespan, its chance to try something new on the world. But time is called and the molecules which make up leaf and limb, heart and eye are disassembled and redistributed to other tenants.