Adversarial writing
Writing, or doing anything else competitively has it's merits. While I try to improve my writing every day, having a competition in mind gives that urge to improve a bit more weight.
If I'm participating in a competition why not try to give my bests. Why else even bother? It gives more incentive to put some extra effort to the writing.
It's also not just trying your best. Often times even that is not enough for the win. What matters is the feedback and learning opportunities you get from it.