First, I disagree with your claim. Unless your definition of "social specialists" is confined to 13th level characters with expertise (11th level for Rogues), the variance in a d20 roll is too large to "almost never fail" on even DC 20 ("Hard") checks.
Second, even assuming your claim is true, if the characters are encountering situations they they would "almost never fail" before engineering the situation to their own advantage, then the PCs are clearly setting their sights way too low, and could easily be choosing harder and more rewarding goals.
Third, if your players aren't all that interested in participating in social encounters anyway, then why does it matter if their characters are capable of doing so?