What you do not realize is that when moderators are appointed, they go through a sort of probationary period with a subsequent review. Just because you are knowledgable on a certain subject or excessively active are not the only determining factors that earn you a position on staff. Conduct and professionalism are some of the other things that play a part in holding the position. Admins and Global Moderators discuss the issues and vote. While sandtiger is very knowledgable, the voting decided his fate. I hope this sheds some light on the matter.
To add, mods aren't added just to keep the forum running or alive. The moderators are placed in their respective forums to perform their obvious tasks, however, do not think that without one, the forum goes unmoderated. There are global moderators in place that govern the forum as a whole. It may take us a little longer to see certain things, but we eventually get there.