There many excellent reasons for the Prime Minister to stay away from Waitangi but being banned from speaking isn't one of them. That's because he hasn't been banned.
The central reason should be that the day and its organisation are a complete shemozzle.
It's unclear who is in charge and what their authority is. Waitangi Marae Chairman and Waitangi Day 2017 co-ordinator Ngati Kawa Taituha complains of "unauthorised individuals" writing to the Prime Minister "regarding the co-ordination of the Prime Minister's Treaty Commemorations Powhiri".
He explains such communication has "created much confusion and uncertainty". He recommends the Prime Minister only "dialogue" with him.
But Ngapuhi elder Kingi Taurua wants the organising committee sacked. "I want these guys [on the organising committee] out. I want these young bucks to get out. I want now the elderly people to take control of Waitangi Day ... I'm not happy at all. A lot of the tribe are not happy."