@ CSSkye - The decision on what threads are stuck or pinned to the top of each forum is determined primarily by the J Mods that use each forum.
Personally, I can see why you might think it would encourage more suggestions for quest lines. However, many wonderful quest suggestions are made where the authors have essentially built complete design proposals, which can run into several posts or pages in length. For them, it is best that they have their own thread, where they don't need to worry about someone posting their own idea in the middle of their posts and where they know that any feedback given is definitely about their idea and not about the quest suggestion posted just before or after theirs. I would be concerned that having a sticky to consolidate quest ideas would discourage the posting of the more detailed suggestions, as well as make giving and reading feedback more more complicated.