I wonder if this isn't a question of who bears the responsibility. For example, in the US you make more money but are expected to save, and make sure you have something to fall on in case of difficult times. In France, you expect the state to take care of you in such a situation. Spoiler alert: depending on the state is not a good situation.
Some people may therefore prefer to be able to spend all they've got without having to think of hard times. Because they may think "it won't happen to me" / "I'll save tomorrow".
As such, I would be very curious to see some actual numbers to be able to do as objective a comparison as possible. Because indeed, if in the US the prices are overall higher relative to the wages, the deal might not be as good in a bad situation. From France, this doesn't seem to be the case, mostly because (outside of SF) pretty much everything looks cheaper. Housing, food, entertainment, cars / gas, electronics, etc. The only issue seems to be related to healthcare. So I'd like to have that actually quantified.
The issue in France is that in addition to the fact that "having a 140k salary is impossible", taxation is very, very high.
If an employer pays 100k in total for an employee, the actual, cash in hand, after income, social security and medical insurance (1) for the employee is around 55-60k. Once said employee has his 60k in hand, practically everything has a 20% VAT [2]. Oh, and since this is France, you also have taxes on taxes. For example, VAT is levied on some taxes related to electricity.
So out of a 100k USD total paid by the company, how much would a US employee have in hand after tax?
I've also noticed that for similar positions in the US (outside of SV) a software engineer can expect twice the salary compared to Paris. And mind, Paris is very expensive for the basics (food and housing).
It would be interesting to see how this compares to professions other than IT. In France, you're mostly barely above minimum wage for blue collar jobs. And minimum wage is nation-wide, the same in Paris and in some village in the middle of nowhere.
[1] Only "basic" health care is actually "free". If you need anything more "advanced", such as dental work or glasses, you better have a "mutuelle", which is basically private insurance. This is usually provided by the employer, but what is actually covered varies.
[2] Food, "necessities" and some other items have a lower VAT, 5.5% I think. There's also a 10% VAT for restaurants in some cases.