Also, Paris is a crime-ridden city that is way overpriced.
From where I live I could work in Paris with the same commute time than I do by working in Luxembourg, but I get a better paycheck.
Renting a 2 bedroom costs 700€ a month where I live, in Paris it would cost 2 to 3 times this.
I don't get the "there's not enough engineering available", this is just not true, reality is that people will earn a lot more in London, Luxembourg, Switzerland, so they chose that.
Not by much [1][2], and rent is worse in London[3]. I think income tax is fairly comparable.
From personal experience the same salary goes further in Paris and quality of life is better than in London, although I never officially worked in Paris so can't comment too much. The nightlife is certainly better. Also Switzerland is crazy expensive so even if you're earning more it won't matter, pretty much everything you buy day to day is about 2x as expensive compared to anywhere else.
[1] https://www.glassdoor.co.uk/Salaries/london-software-enginee... [2] https://www.glassdoor.co.uk/Salaries/paris-software-engineer... [3] https://www.numbeo.com/cost-of-living/compare_cities.jsp?cou...