Currici - wiki for education

The most popular wiki is ofcourse wikipedia. I stumbled upon another wiki for educational content: curriki.com . There is not much content yet, but it is a good initiative. It is not the first project trying to share teaching content. I'm wondering if it will work. I don't know why but there is something going wrong with the whole content sharing for learning. It doesn't seem to happen. As always many takers, few to no givers. Why does everyone keep sitting on their lessons? Is making learning content something to personal to share? Is it something you only want to share with your direct colleagues and not with the world? Do teachers fear the reactions of their peers? Is it too much trouble to share? Is it more trouble than it is worth? Please teachers of this world, enlighten me...