You realize this is a feature, not a bug, right? The threads with labels that say "wiki" are regular threads that happen to have a wiki attached to them. Many of these threads have dozens of pages of posts. Attaching a wiki allows the collective wisdom of the posters to be distilled into useful information. Not everyone reads FT every day and even those who do don't read every thread. A lot of traffic to FT is people looking for the answer to a question. The wikis at the top of popular threads help them find that information more efficiently.
Just as an example, one of the threads with a wiki near the top of the page today is
http://www.flyertalk.com/forum/ameri...ilability.html, which has 272 pages as of this post. I don't think I've ever been in that thread, so if I wanted to book a F award on CX I would be very happy that the wiki is there, so I don't have to look through 272 pages to try to find where to start.