Many of the tags were added long before there were many posts at all in the forums.
As the forum grows I am sure that there will be more added as well.
As for the number of posts versus the number of visible posts, that simply comes down the the permissions.
Every forum has areas that are used by Admin/Moderators, etc; in the background.
Each tag was tested in such a forum, and that is why some presently don't go anywhere in the public forums.
We have done a lot of testing in the background, simply to get the forum ready for everyone and make sure it works as intended.
If you could make that "Ignore" feature affect the "Recent" listing, it would be really perfect. There is no logical reason I would want to see recent posts of fora I've chosen to ignore, it just clutters things up.