What is that drives people to do amazing things? Why do writers write, why do painters paint, why do movie makers make movies, why do photographers capture images?
In nature, outside mankind, questions like these are very easly answered. Animals, do things motivated only by insticnt. But, like the myth of prometheus tells us, Humans, because they weren't strong nor fast, were given fire (wich stands for knowlegde).
Therefore, Humans, because they are equipped with knowledge, have the hability to make their own path along life. So it is fair to say that, among all the animals, only humans have free will.
This leaves unanswered the questions in the beginning. So now knowing that only Man has free will... Why is that we choose to do these things? Is it just human nature? Or do we do these things socially? Well, it can't be just by instinct, because otherwise all animals would make art. So why is it that Man bewaves in this way socially? Would a man/woman outside of society come up with art by themselves?
It is my opinion that art came to be in many different places and not just one person that came up with it. And that is why one writer might write for one reason and a different one for another. Same with a painter, a movie maker, a photografer, a musician, a dancer, a sculptor.