Chasing a ball, professionally, for millions of dollars a year, gives some very rich and famous humans a sense of purpose.
Laying on a beach and surfing may fulfill a sense of purpose for other humans.
Some humans need to solve hard problems.
Some humans need to create something original.
And then a lot of humans... most humans... drift through life without any sense of purpose. Does work, the need to work, give them some? I'm not a Calvinist, but I have to live in a world where most people are like that. So if they don't have some need to do something, idle hands are the devil's plaything, and no good can come from the idleness. Just drugs and dissolute degeneracy. Take it from a creative alcoholic who struggles with the question of purpose myself, and finds some light between music, painting, hard work I have to do and my better angels.
That's what you're having a hard time fathoming, because you think everyone is like you; imbued with meaning and purpose that they will find. They are not. Even those of us who are, or were, don't always remain so.
But need? Need wakes you up.
The crush. The urgency. The do or die. The death-defying situation. Sinking or swimming. Here is what brings out the initiative and the creativity and the purpose in people.
I used to believe exactly what you said when I was 17. If we didn't have to work we'd all use our free time to make amazing art and poetry and contribute to humanity.
Look around, man. I know a lot of people who don't have to work. Half of them are homeless and the other half are millionaires. You know what none of them are doing with their free time?? Anything resembling something with a purpose.