France is currently ruled by the Socialist party. There is a methodology adopted by the socialist parties all over the world to retain power.
Tin foil hat time, eh.
It is like this:
1. Tax to death the 10% hard working people and squeeze as much money as possible.
2. Give this tax money as benefits to the remaining 90%, lazy people.
Let's just dispense right now with the notion that how much money you make is proportional to personal effort. That is an insult to school teachers, police, scientists - well, pretty much anyone who earns a wage for services.
That is not to say that capitalism isn't the best engine of economic growth available, just that it has little to do with fairness. The idea that everyone could be a fantastically wealthy hedge fund manager if they just worked hard enough is patently false, but that's the implication that is made when you equate wealth with hard work. Certainly it's easier to be wealthy if you work hard, but then again that applies to any goal in life.
That said, looks like this French law is temporary - 2 years. I suppose they figure that's short enough to prevent companies from relocating.