The pay difference is not a factor 2. You are paid 300-400% more than in the EU easily in the US, and the difference grows if you compare net pay vs before-tax. Cost of living bay area vs center Paris is a wash. Hell, I'd say the food is actually cheaper in the US. Frankly, unless you know your way around to avoid tourist places, food is cheaper
and better in the US compared to center of Paris, although I'll agree that if you look around you can find much better in Paris than in the Bay Area.
And if you're employed, especially as a SWE, medical care is better in the US. If you're not ... EU >>> US.