The reason might be that they had their entry lying around and the cost of entering the competition was very low.
This appears to be true of writing anthologies; it's pretty common that Amazon is running a sale on some anthology or other that advertises an incredibly high-powered list of contributing authors. But the quality on these is lower than you might expect.
I understood why when one of Brandon Sanderson's blog posts mentioned that he was solicited to contribute to one of these that was raising money for some charitable purpose, and he sent them a piece of writing he'd done for a different book that hadn't made the cut to be included in that book.
