Board Thread:Support Requests - Getting Technical/@comment-222.127.119.24-20150818083656/@comment-17725354-20150818231616

You must first have an account with sysop (admin) privileges in order to edit MediaWiki pages.

If you already do, then the reason is because Wikia temporarily disabled editing for MediaWiki pages due to recent security issues. Hopefully, editing of those pages will be re-enabled soon, but Wikia hasn't given any specific dates as far as I am aware.

EDIT: Wikia is unlocking welcome-message pages in the upcoming site update.