Flickr is set-up to sell prints, why can't I profit off my work?

So I can buy prints from my flickr account. I'm also paying Flickr for a pro account. Why can't I make profit from my work if I allow others access to buy prints? I did see the Flickr FAQ entry about not using Flickr for commercial purpases, but money is already changing hands, just that Flickr/Yahoo gets it all.