The best talent that offers something special has no trouble attracting far more than $80,000/year in Canada. The people being offered $80,000/year are not the top talent that you speak of. That is an average, representing the average.
And for average people, that's a feature to see them leave the country for places that need them more. Again, we simply don't have enough work in Canada for all the tech people Canada is producing. We, as a society, put intense pressure on our youth to strive for careers like these and as a result we are pumping them out at rate that is well beyond the actual need for them (domestically).
If everyone who is capable of tech work that came up in Canada remained in Canada, the job would be quickly approaching minimum wage for an average worker. The fact that we have so many leaving for the US is the only thing that has allowed us to maintain something as a high as $80,000 average tech salaries.