I created one entry for the career-advice wiki tag, and decided to see if I qualified to create any others. According to the "top users" link for a couple other tags, I appear in the top 20 answerers for a couple others, for example "best practices" (oh no, I'm at the bottom of the list!). There is no edit functionality for me when I try to edit the wiki tag for best practices.
The top users page always shows the current user, even if they're not in the top 20.
Take another look at that page and count the number of users displayed. I suspect that there are 21, with you at the bottom. It can be difficult to tell - especially if you are outside the top answerers in the last 30 days as well - and I believe has been raised on Meta Stack Overflow before. If I find the link I'll update this answer.
I believe there are other rules aside from just being in the Top 20.
When the Tag wiki concept was launched, you also require a certain about of up votes for that tag as well:
Tag wikis help introduce newcomers to the tag. They contain frequently asked questions about the tag and guidelines on its usage.
Tag wikis can be edited by users with more than 2000 reputation, provided:
- They are in the top 20 answerers for this tag or
- They have more than 100 answer upvotes in this tag
I believe the exact rules have changed since then, but I can't find the current rules to be more exact.