What this article has done is outed all the Canadians on HN. Hey hosers!
There is no reason other than the US teams just happen to have drafted better, hired better etc. Nothing to do with economics as there is a hard salary cap.
Edmonton won the lottery this year and will get McDavid. Maybe that swings the tables. Had a Canadian team won the lottery the year Crosby was drafted, maybe that changes things.
Not all trends are explained by stats.