It was more the incompetence and possible treason of Charles Huntziger.

The Maginot Line was only intended to delay an attacking army. It wasn’t going to stop them on its own. So, when it was attacked the army needed to gather its forces and counter-attack before the Maginot Line fell. But, when the Germans attacked that didn’t happen. Not only that, but before the attack, Huntzinger stood out for being one of the few generals not asking for more troops to reinforce his position.

It’s hard to believe that Huntzinger was that incompetent. So much so that some historians think that he was actually a Nazi sympethizer and intentionally caused the French collapse. That might just seem like French historians diverting blame. But, Huntzinger not only failed completely at stopping the German invasion, he was also one of the first who was pushing for an armistice, then he also somehow became the person who met with the Germans and signed France’s declaration of surrender. Then, during the Vichy regime, he was a promoted to an even higher position.