Board Thread:Support Requests - Designing Your Wikia/@comment-1264853-20160602111838/@comment-27073024-20160603194221

The main navigation is limited to only a few links because it fits well with displays of different resolutions, including tablet users. You can: Whatever you can't fit in the drop-down, simply include another "More..." link to a page that contains all of the seasons.
 * Include only the most important links.
 * OR, have the last link say "More..." and have a drop-down menu filled with the remaining seasons.

Take a look at the Extended Navigation script to see if it can help you a bit more.

Cheers!