hmmm... could be the topic is a little obscure and not so fun.
also the huge wait between the last one that had so much momentum likely didnt help.
given that most people i'd assume throw an hour to this after work, during lunch, or between real paying gigs, i'd think that you'd get better turn out if it was something more fun that could be sketched or designed without as much "thought".
not saying it should be merely a styling exercise, but coming up with completely new solutions to huge global problems is kinda pressing (and depressing) to do in 1hr.
sometimes design can be good and still simple. i've never found a good toaster for example, and would kill to design a better iron. either of which for example could be something to do in 1 hr with a few sketches and a bit of clever thinking about the use/user. starting from scratch like the bag (and to some extent the water thing) is just is a lot to ask for, and you also seem to end up with not so hot submissions that are focused more on the solution than the "design", presentation, sketch that i would think could be the focus on the 1hdc exercise.
R