"Is this a matter about which they claim some sort of special knowledge which, on their view, Rome lacks?"
Not lacks, rejects.
Have you read Saint Pius X on modernists? SSPX holds that the modernists continued what Pius X saw them doing, and by the middle of the 20th century had gained enough influence to steer the Church away from authentic tradition.
Think of it as similar to the way leftists in America have gained ground step by step, until now we find ourselves completely divorced from the principles on which the country was founded.
After all, leftists and modernists both take their marching orders from Satan.
Thank you for sharing this insight. I agree completely that many acting in Rome's name (those invoking the so-called spirit of the Second Vatican Council come to mind) ignore or trash Tradition. But this is not what Fellay said. He is saying that Rome needs to be taught Tradition's raison d'etre. What does the Society teach is Tradition's raison d'etre?