Us is so outrageously better than the rest that people fly across oceans to start businesses there. Canada, being next door, doesn't have the distance moat to at least slow down the brain drain
A small crew of people could potentially build the next WhatsApp. On Erlang.
I know people from "first world" countries like Japan and France that are come to work in the US simply because it pays much more.
For many reasons, only some areas succeed whilst the rest fail. In this case, Canada doesn't have silicon valley, nor do they have a high amount of start ups.
I'm spoiled by walkability and quality cycling infrastructure.