The notion of purpose, I believe, comes from the desire to deny admitting the insignificance of humans and of Earth, compared to the Great Void that contains everything in existence - the grand elephant in the tiny corner of our brains.
When we seek purpose, we seek to escape admitting that we are insignificant beings, and when we actualize the purpose which we seek, we have “evidence” for ourselves to “prove” that we are not tiny, insignificant beings.
Everything that we do to confront our subconscious denials, we do through escaping, escaping from the possible one day where we would have to confront our fears and anxieties and admit insignificance. And, thus, we go on metaphorical and non-metaphorical journeys to further fortify ourselves from submitting to our subconscious fears and anxieties.
To constantly seek purpose to counter-validate our primal fear of insignificance, is equivalent to a materialist constantly seeking wealth, to counter-validate their subconscious fear of social rejection.
This escapism is important for human beings because we as human beings are afraid to confront our subconsciousness in solitude. We are afraid to do so because once we’ll admit and be honest about the beliefs we subconsciously hide, our perception of life would never be the same.
This is why Silent Hill, a video game series of psychological horror, is indeed horrific and spooky. Take the second game, Silent Hill 2, for example, where the protagonist, James Sunderland, eventually realizes the cold truth about his dead wife the more he ventured deeply into his subconscious, in the form of the ghost town of Silent Hill - he wanted his wife to be healthy not because he deeply cared for her, but because he wanted to f*ck her, and this sexual frustration has lead him to kill her, as a form of catharsis to his repressed libido.
The same applies to our lives; there are many truths about ourselves that we have learned to deny, and we may live an entire lifetime just to reinforce the things that we deny, so the chance of confronting our denials head-to-head would decrease significantly. One of those truths is that we may subconsciously believe that life is absurd and that we are insignificant beings, hence why we seek purpose - to reinforce our self-denying, completely honest beliefs.