When there is only a single Wiki, and someone comes along knowing something that they want to put in the Wiki, but they see that someone has already said what they want, but it's not exactly their words, they just drop their idea of adding to the Wiki. They think, "Oh, someone already thought of this, so there's no need for me to add what I know." This is why there should be many different Wiki's, so the person can get several different points of view about a single topic, and possibly add their own p.o.v about the topic. Besides, I like posting material that is new to the site, it makes me feel like a closer member of the fansite community.