Answer:
Geography, French failure
Explanation:
A) The French didn’t wasn’t to fight and so their Morale was garbag, which made them easy to attack.
B) The French were conentrating most of their resources on ther Maganot Line, which made it easy to go around, like the Germans did.
C) Amphibous Assaults are EXTREMELY hard to pull off. At that time the British stil had a decent fleet, which would have made attacking them hard. All the Germans had to do to take Paris was go through Belgium, through a super dense forest, and then sweep the French to reach Paris.