Why Btonze Age?

[Anomalocaris]

Interestingly enough, the French armed forces ran wargames in the Ardennes in 1938 which showed that a tank breakthrough through that area could be completed within three days, the actual German breakthrough took 57 hours.

Yeah. The forests were impenetrable. But they had these things called "roads". Not sure the French knew about these "roads", but the Germans did.

It's not as simple as knowing whether there are roads.   It takes one good quality road to support just a single Corp on the offensive.  A major land offensive would involve hundreds of thousands of vehicles.  Tracked vehicles like tanks quickly tear up most roads. So requirement for supporting an mechanized offensive is even higher.  The French didn't believe the number and quality of roads in the Ardennes were sufficient to support more than a couple of division.

One thing the Germans really were exceptionally good at during WWII was organizing effective improvisation. The Germans did organized a logistic miracle to get the vehicles through the Ardennes. Even so, they ran a colossal risk because for 3 days, the created an enormous traffic jam inside the Ardennes. If the French airforce attacked the jam, the Ardennes offensive would in all likelihood have failed.