My wild guess is they're just not confident (...or interested, if I'm being a little cynic) to do anything outside stereotypical straight or spiky anime hair - it's easy, popular, unisex, low rez, few textures, and nearly no clipping. Hopefully if/when there's another art contest, more entries will have a bigger variety in hairstyles other than 20 variations of Karen hair, I honestly don't want to see any more of those...