I work at a global (nominally European) company with some of its largest offices in Europe. When I have floated the idea of hiring in Europe instead of Seattle, because of wage costs, I have been informed that it doesn’t save much money despite the wage difference. The employee overhead in the EU is (to my USian mind) astonishingly high. The UK is not as bad as the continent, but I floated that too and was informed it all washes out the same.

In short, the apparent arbitrage opportunity doesn’t actually exist. As you would expect in any semi-liquid, semi-efficient market.