This is because:
1- there's always room for improvement. If you lose a competition, that's a good reason to create something even better for the next one.
2- the best is not always the winner. Kinda obvious, no?
BTW, you're improving and learning new techniques. This should be something you do for yourself, not to win a competition at a forum. If you see things from this point of view, this wallpaper helped you to learn something you didn't know maybe, and this means your time at least was not completely wasted.