Well... contract renewals aren't being based on juventuz forum opinions. De Sciglio got a renewal because Allegri wants him to stay. And as long as Allegri is in charge of Juventus, Rabiot will be playing. He really likes that player. I'm just stating the obvious here.
Just like it is obvious that Allegri wants Rabiot to stay, it was obvious that Allegri didn't want Dybala.
I'm not justifying Rabiot wages by the way. I'm just pointing out that he is the first name on paper when Allegri sets up his midfield. And unless we get three amazing midfielders, Allegri will want him to stay.