User blog comment:Kaido King of the Beasts/Chapter 818: Stepping Stones to One Piece/@comment-4374114-20160303195953/@comment-10543621-20160304014817

Yeah I have a feeling not many people knew about Robin's ability to read the poneglyphs. People that did know were all actively trying to hide that secret. It seems that maybe it was by pure luck that Crocodile managed to discover her ability to read Poneglyphs. But he sure as hell isn't gonna tell anyone that.

Also, I'm thinking even if some other big power knew of Robin's existence, they probably wouldn't want to risk any big movments in paradise to capture some unknown girl. Afterall, the Yonkos are mostly active only in the New World. Any major movements in paradise is sure to be fishy as hell and draw others attention. So I'm gussing, if they knew such a secret, they'd wanna keep it hush until the time is ripe or something...