In regard to planes, planes in general are a lot more expensive, fewer, and thus easier to track than are people on foot. Regarding the Maginot line, it actual

In regard to planes, planes in general are a lot more expensive, fewer, and thus easier to track than are people on foot. Regarding the Maginot line, it actually forced the Germans to use the Ardennes. This was a high risk move for the Germans and if the French had been doing what they were supposed to be doing, they could have destroyed the German Army in the Ardennes. So, the Maginot line actually was useful, but the French failed to exploit what it was doing for them.