A. The person is hired to create something.
B. The person creates something that's not easy to copy.
If you were hired to design a set for a play, you would get paid for your work. If you created a physical three-dimensional sculpture, someone else could try to imitate it, but the imitation wouldn't be a perfect copy. That means your original sculpture would still have value and could be sold. On the other hand, if you, on your own time, created something that cost nothing to copy, such as--oh, I don't know--a picture of a sunset, you should not expect to profit from selling it. It wouldn't matter how much time/effort/money/energy you put into creating it.
So, what's going on with SOPA then? The government realized that they don't have the resources to police the Internet for copyright violations. Of course they don't. It's impossible. So now they're attempting to foist that impossible responsibility on website owners. I have no idea how the bill is worded, but I can't imagine a scenario where the wording could be "fixed" while keeping the intention. The intention is broken. Copyright law is broken.
Copyright should be non-exclusive. Anyone should be allowed to copy anything for free.