I agree a million percent. Especially when you have no interest in the last weekly challenge of the group, that's time I could have been using towards one of the new challenges. Of course, there's always other stuff I can do, but DI building is kind of a fun ritual (I'm sure I don't have to explain to anyone here). I've been working on a secret project in the mean time, but I really wish they would update the list every time the current challenge is over.
As to people skipping the challenges, I can't speak for everyone but if I don't get a 'spark' from a challenge, I don't compete in it. With advanced notice though, I may get a spark before the challenge week arrives. I just look back at my thoughts when this current group of challenges arrived, there were only two challenges that initially made me think 'ok, I can try something for that...' But with a little time to think about it, some of the other challenges gave me ideas too.
Plus I really wanted to support the Sheriff's challenge