Because we are afraid of death, of the annihilation of our everything it brings. So leaving a legacy alleviates that a bit - we die but we are not dead-dead as

Because we are afraid of death, of the annihilation of our everything it brings. So leaving a legacy alleviates that a bit - we die but we are not dead-dead as long those memories are alive. For some it will be an immortality project, for others a silly endeavour, but I say as long it makes one happy (less scared) let them all have it.