I assume you're meaning in the defence of Germany post D-Day. It's actually very simple. The Maginot Line was a superb set of defensive fortifications, set up opposite Germany. The Line was composed of various lines of fallback positions, and it was done in a very specific order to defend from an attack from Germany. At the back of the line (the French Side), it was primarily composed of artillery positions and supply depots. At the front of the line (near Germany) were a series of enforced bunkers.

So if Germany actually attempted to use the Maginot Line, they would be using what was literally a backwards defence mechanism. The Line was not designed to defend Germany, and it was not largely capable of doing so effectively.

In addition, the large guns pointed at Germany, and were not designed to be turned around. The tunnels could have been used as temporary bomb shelters, but that was it. In addition, aircraft, which was not widely used in WWI, made the bunker defense useless, along with fast moving armored tanks.