The port of Brest was occupied until the end of the war. And Caen wasn't the only place that got hammered into rubble. The rail lines and locomotive stock were trashed. The nazis had deported a lot of their working age men for forced labor as well. "600,000 to 650,000 French workers were sent to Germany between June 1942 and July 1944." More than 75,000 jews were deported and 72,500 of them murdered. Military and civilians deaths were 567,600

Those kind of things really hurt your GDP. There were also quite a number fighting in Free French divisions who weren't working. This is very similar in ukraine right now. They've got men and women serving at the front and in the military who are not contributing to normal economic activity. Ukraine is fighting heroically but it comes at great cost in so many ways when your country is a warzone. That's why it's so important to continue aid in not just weapons but financial support.