1) In France, your salary is usually lower because your employer has to pay a lot of taxes. So does the employee.
2) Those taxes are in turn used for a lot of things that make the French model (and those of Sweden, Denmark, etc.) a nice place to live like next-to-free education, health care, transportation infrastructure, public libraries and hospitals, universities, so called "Grandes Écoles".
I'm not saying the system isn't currently broken or that it even works but in the end, it is really not as simple as X in France and 2X in the Silicon Valley cause in the end, you have to shell out for your health insurance, your education and a lot of different services that are just part of the French package when you live in the USA.
A good illustration of this is the price I paid to go to one of the best universities around Paris: the equivalent of $250 a YEAR.
For that kind of quality, I would have easily paid something like $5000 or more in the States.
So really, both systems have their pros and cons, it's really way more nuanced than that.