People don't read the rules, or simply ignore them. I delete non-conforming images. I email the most egregious offenders. It's irritating.
I offer contests mainly to get inspiration for some particular theme. The rules are always clearly stated, and I'm always looking for quality work, something that better than what I do. Most entries are ghastly junk that I wouldn't tape to the inside of a gym locker, much less hang on my wall. But I usually get a few real gems.
And then comes the voting. People lean heavily toward backyard photos of domestic pets, and oversaturated sunsets, and many people will solicit votes even when asked not to. Frustrating when poor quality images come out on top.