I'm not sure he would have, but that was the only way into France for a large army. The Ardennes was a no chance idea. Belgium? Well we all know what a flat God-awful place that is to fight, something that Hitler, who served on the Western Front had to remember. I mean the man was clearly half a bubble off plumb, just look at the insane laws he pushed through before he died drooling at the supper table, but he couldn't have actually been that out of touch.
I was playing Germany in HOI III one time and ran the following simulation for a battle against France:
-Send infantry divisions into Belgium and the Netherlands (for more bases against Britain). The Allies pushed into Belgium to try to check my forces.
-Maintain infantry divisions on the Siegfried Line to hold (but no advance against) French soldiers on the Maginot Line.
-I combined six armored divisions and four mechanized infantry divisions into one force and sent them across southern Belgium. Then I had them turn northwest and push towards the English Channel.
-Once the armored forces reached the English Channel all Allied forces in Belgium had been effectively cut off. I was stunned to see that the AI hadn't left a sizeable reserve in central France.
-Once I liquidated the Allied divisions in Belgium, I reorganized and sent my armored divisions to seize the Channel ports while the infantry divisions advanced south and cut off the French forces in the Maginot Line.
-France surrendered about six weeks after the campaign began.
Not sure how well this would have played out IOTL. Surely the Allies, in this situation, would have left enough forces to deal with any potential armored thrust towards the Channel.