I'd say the main reason people badmouth France: not easy to corrupt easily. People can try ( foreigners have tried to import there their corruption systems), but sooner or later a clean up takes place. And many are actually agrieved who have to deal with French judges ( "karachi" affair where even Menaker was "interviewwed", etc).
Also, London is well known to be a place to launder money, this would be difficult in France. Yes, the employment laws are such that French citizen would not hesistate to report you discretely : you can't corrupt them via fear of unemployment.
Another reason people badmouth France: after robbing their own nations of its wealth, unfortunately when they come to settle in France, the citizen do not approve of showing off money robbed to the population that later shows up as refugees. The oil shecks from the Middle east are closely associated in the psyche with the poor asylum seekers from these same regions. The Russian oligarchs are said to have made their money via dismanteming Russian people's assets. French would not tolerate French politicians and their families robbing the taxpayers to go and live the high life overseas : so why should French people accept foreign politicians and their families doing so?
Also, the type of crimes committed in the UK would be difficult to commit with impunity in France.
It would be very questionnable for a Russian to be assassinated via polonium by Russian oligarchs on French soil, and the oligarchs responsible being left scott free, like it happened in London.
And actually, after the 2008 financial crisis, some London traders came back in France as unemployed and none of them spit on their generous employment benefits given by the French government when they returned. They did not need to go and work as taxi drivers like US traders had to.
And lately, France is looking to change its laws regarding "rich" foreigners ( including middle east officials) who when ill shop around and discover that France has one of the best medical care in the world. France is no longer going to tolerate them using the French medical system for free like they are also citizens. When ill, they don't badmouth France, but run there forgetting that this system was hardly won by its population.
Let's just say, France has different set of values : no anglo-saxon value system, just different.
Now, all said :
all legit business, all clean money, all business practices that respect the employees are fully welcomed to France. The really generous business subsidies are there. But only for legit stuff. And Amen to that. Nice to know there are few countries with real values, and not just kissing foreigners' a$$ for $$$.