Major US tech companies earn a profit-per-employee of $200-400k[0]. That's across every employee, so depending on how you attribute value the profit-per-SWE is much higher. That gives a lot of headroom to drive up salaries when competing for hires, and in part sets the market price. I suspect that low European software salaries are just a function of low profitability of European software companies. e.g, spotify is (…
The value engineers for US companies generate is higher than the value engineers for EU/CAD companies generate, so they have a better bargaining position.
This is probably because US companies have a bigger market to start in, and have been more successful at expanding into other markets (including EU and CAD). The profit of tech companies is constrained by size of market addressed, not number of employees they hire.