Mostly because despite the massive growth in population and immigration, there isn't the equivalent in housing or jobs. Salaries still suck back in Canada, and if you're a White Collar Canadian citizen, it's better to just work in the Bay Area or Seattle indefinetly on a TN Visa (clearly you can see which part of Canada we used to live). The US can easily absorb the amount of immigration Canada is seeing, but a country that has around 10% of the US's population and a GDP that's around 5-10% of the US can't