I would say it's more because they had put a lot of time and effort into their work. And it can be frustrating when you see some badly traced works, which are based on something you did. Though I always thought of it as a compliment when people wanted to use my works as reference of any kind. So... can't say I get them 100%, when they are against it. d:
My favourites are the ones who are like, "(C) Me 2012. Do not edit, copy, repost, or distribute without my explicit written permission"...and their art 99% of the time is complete shit. Like anyone would want to copy a wonky-ass MS Paint doodle.
But seriously, most of the people on here are tards who don't understand copyright. They think that their half-assed Photoshopped animu bois are going to land them big in Japan so they are paranoid about people ~STEALING THEIR ORIGINAL IDEAS~ while at the same time failing to see their own incompetence. People who scream about "U COPIED MY POSE" are off their rocker--like they have anything original worthwhile to share to the world.