The Catholic Church won't even apologize for its role in the organized killing of over 150,000 people in Yugoslavia in the 1940s, and they were white and Christian! So why would it apologize for this?
First nations leadership are as responsible for the individuals committing these arsons as white nationalist politicians like Donald Trump and media personalities like Tucker Carlson are for the terror rampages that white supremacists commit across America. To hold them to account for this is an exercise in hypocrisy. Until several months ago the only senator from my region was notable for repeatedly insisting that residential schools were good and no one pointed at the national culture and said "Bad!" Well, I did, but you guys didn't like that.
A lot of people are angered by this and traumatized by having it brought up again and again and we don't really have a national strategy to help them cope, so of course these outbursts are happening. They also happened in the past (churches being burned down on reserves is uncommon but not unheard of), and they will continue to happen.