Life is a fleeting thing, that is if you are a mortal who does not cultivate. But for those who do cultivate, life goes on for as much as you raise your cultivation.
By the time you reach Saint stage your lifespan already reached 500 years. If you reach dominion realm, you will be able to live for thousands of years.
Humans were the kind of race where they wish for life as they envied the long-lived race such as the elves and the spirit beasts.
Elves were known for their ordinary lifespan to be as long as 500 years in the shortest. That is them not cultivating. Elves were originally people of nature, their life force was much greater than any other race.
In the end, what this boils down to is that humans longed for a long life so they can find possibilities for themselves. But if one has to suffer for millennia with the memory that haunts them awake, is living be better than dying?