Blame Canada, Or, the Myth of the Shallow Talent Pool
medium.com
medium.com
And the CS students coming out of Montreal universities are excellent (and bilingual). Plus there are generous tax incentives for R&D.
Sure, it's not ideal living in a foreign country, but while I don't have dependents or large liabilities to pay off, I'll enjoy getting a salary which is literally double what Canadian companies have offered.
As for the cost of living. LA is cheaper than Vancouver. So are many US cities. The article seems to treat SF as the whole of the USA when comparing costs.
Not everyone that is talented will move to the USA, but you better believe the prospect of literally making 2x the pay is worth it to most people. Especially when most talent is hired right out of school before they start putting any real roots down.