Think about it...people can invest maybe $10 or less to buy a high resolution image or vector, then open their own website. Then sell them for even a little less that the big sites. In most instances, they only need to sell one or two of that image to recoup their investment, then the rest is gravy. Since copyright infringement enforcement is so lax, they might be able to get away with it for a while and make a nice little chunk of change. Sure, there's web hosting costs too, but they might already have that anyway.
Why get paid pennies from the agencies when you can make dollars off of somebody else's work!
