Why didnt Gilberto Ramirez fight in the WBSS?

The simple answer would be because of Bob Arum. The more complicated answer would be that, shy of Arum convincing ESPN to carry the super middleweight tournament, he would've been left at the mercy of Sauerland Event in a tournament featuring some good fighters (Groves, Eubank Jr, Braehmer, and Callum Smith have all shown ability) with a fighter that he still doesn't really know is the true article. Too much risk, simply put.

Bob Arum of course.

I feel as if you answered your own question