The Loremaster didn't appear last ESO Live, so that leaves us to speculate: those of you who played last year recall that the Dunmer New Life Festival quest is a dance developed in reaction to dancing being forbidden. So why was dancing forbidden in the first place?
IMO it almost requires the Tribunal to be involved somehow, as they're the only authority with enough power to make such a decree and make it stick. As it seems contrary to Vivec's established persona as the Warrior Poet to take issue with one of the performing arts, and Sotha Sil spends most of his time locked up in his personal pocket dimension, my money's on Almalexia for the culprit. But that's speculation on my part, and anyway doesn't answer the why question.