Hall of Fame
The Nole Slam isn’t an "official" achievement and it’s not as impressive or difficult as the CYGS so there’s that. And as long as Federer and Nadal will be in the picture, they will shift attention away from his achievements a little bit because he has to share the limelight with them.
If Novak was Nike's client, Nike's PR-activities would ensure Djoker Slam was widely known. But Novak's sponsor was Uniqlo, who neglected the promotion of his success.