For me it's because SyFy re-aired Jurassic Park (which I watched the last time they showed it) instead of a new disasterously cheesy movie that I do not have high expectations for. But I will trade Riddick on SwapTree and hopefully get something better.

I wasn't interested in the Girl With The X series anyway, but it is possible the movie screwed up a good book* (it wouldn't be the first time).

*If you like that sort of book, which I dont, because taking place in the Real World™ type stuff is not what I look for in a book.