User blog comment:Kirkburn/Technical Update: January 27, 2015/@comment-3183960-20150128123305/@comment-452-20150201233631

You can read why here: User_blog:Daniel_Baran/Search_Developments:_Big_Picture
 * edit: and here: User_blog:Dopp/Updates_to_How_We_Search

My assumption at the time was that they wanted people to see the ads on the search page, and it also increases raw pageviews, which is good when advertising wikia to advertisers.

We had to fight to get them to just add the option to let us keep Go search at all.