The majority of Indigenous women and girls seem to be leaving home to acquire education and work.  That has been proven in many studies already;  this one is from 2011: http://www.thecanadianencyclopedia.ca/en/article/aboriginal-people-urban-migration/

Additionally, most Aboriginal people already reside in cities, and have for a long time, and yet they still tend to disappear and/or get murdered at a greater rate than their female peers on reserve: https://nwac.ca/wp-content/uploads/2015/05/Fact_Sheet_Missing_and_Murdered_Aboriginal_Women_and_Girls

That certainly undercuts the notion that the problem lays within the reserve community.  Many a settler wants Aboriginal women to move to cities, often -as we see here- citing increased opportunity.  but we must ask ourselves; What kind of opportunities?  To get better education or work, or to be victims for those killers living within cities?