And more than that, the Maginot Line was as extended as you were going to get it. Because any attempt to fortify the Belgian border would have enraged the Belgians, since they didn’t want their land to become a battlefield between Germany and France yet again.

So his proposed plan would, at best, have weakened the French position, and at worst would have lost them allies, and maybe even seen the Belgians join the Germans on the grounds of “I now have axes to grind”, instead of being another Allied Power.