User blog comment:Rappy 4187/Technical Update: March 10, 2015/@comment-28122555-20150312174212/@comment-452-20150318230647

It's automatically activated on wikis they have paid content for.

So apparently, SpikeToronto, the video ad hosts that wikia has agreements with don't have any videos relevant to the subject of the wikis you use.

Not that it needs to be relevant, video game wikis get videos regarding different franchises. :(