It's you they don't like
The political elite in France have a problem with what they see as the creeping Americanisation of Europe in language, culture, defense and above all else capitalism. We are your Trojan horse. President Sarkozy used to call it the "anglo-saxon way of life" particularly "anglo-saxon finance" and capitalism, he was desperate to destroy it in 2008 and extol the virtues of the French way.
In recent years President Hollande ramped up tax on the rich and David Cameron rolled out the red carpet and invited them all to flee the tyranny of the French tax regime. It wasn't even subtle and irked the French government, reiterating to them the difference in way of life, the low tax predatory Anglo Saxons. London became the 2nd most populated French city and Hollande will be eager to get revenge, to damage the UK. He won't be President much longer but Macron was finance minister when David Cameron mugged them off so he will be looking to get a win or two.