Legality is an issue in some countries. A lot of "exposure" is done without real consent, which is pretty scummy, and sites can't verify on every single image.
I experienced the same issue with eBlue. I'm sad I can't post my photos there unless i pay a fee. But I can still view the Timed Images posted by other CDs, and extend their time of exposure and/or repost their photos to Twitter or Reddit.