Well, NSLB and Eclipse Phase never asked for anything. If it's freelance work, they don't like writers turning in more than was asked for.
As for No Security, I wrote two short stories: To Bright Boy and a piece about the companions. Both were rewards for backers.
And they were, by orders of magnitude, the least popular rewards. Unless you have, like, Pathfinder market share, game fiction doesn't sell well enough to justify the time it takes to write it well (at least for me). Hell, most people that by game books don't read them in their entirety. Most people, in general, don't read at all. And there's a lot of really terrible game-related fiction out there (mine may be among it), so you can't really blame people for not wanting to be burned again anymore than you can blame people for passing over the movie tie-in novelization of something.
Granted, I'm going to finish the Red Markets novella and hopefully offer an audiobook version of it as a backer reward, but I started writing it for myself, to get an idea of what the setting was all about on the ground level.