NB has 7 of 10 lowest median income Postal Codes

I came across a Vancouver Sun blog that posing in its title: Is Vancouver's Downtown Eastside really "Canada's poorest postal code"?

The blogger linked postal code information to Statistics Canada median income information and found out that New Brunswick has seven of the ten poorest postal codes by this metric, including the poorest E9G – the Burnt Church First Nation.

Unfortunately, but not too surprisingly, most of these NB locales are home to first nations groups. 

I wonder, why is it that NB’s first nations communities have such low median incomes relative to the rest of Canada and the rest of NB?