For Lord Gort - it wasn't his country, he'd only been appointed to command the B.E.F. the prior September, and he'd been shuffled through a lot of different jobs in the prior decade. (Including time spent in China and India - hardly useful experience for WWII in Europe.) Still, Gort and his immediate subordinates got their sh*t together, moved fast and made good decisions in very new, chaotic, and challenging circumstances, and did extremely well.
For Gamelin & Co. - it was their country, defending it against a German invasion had been their d*mn-obvious Job # 1 since at least the German invasion of the Rhineland (March 1936), and they'd been building the Maginot line since 1930. Yet their performance in the event was laughably slow and weak even by the 1914 standards of French General Joseph Gallieni. (Who had been recalled from retirement, was in obvious poor health, and had served most of his career in French overseas colonies.)
https://en.wikipedia.org/wiki/Battle_of_France#Central_front
Quick summary: The French Army's high command was stuporhumanly slow and weak in their response to the German attack through the Ardennes (just north of the north end of the Maginot line). Especially considering how quickly the German Army had conquered Poland less than a year earlier. And had conquered Denmark just one month before. And was wrapping up the conquest of Norway at the same time as they started attacking France...
If you know in advance that your soldiers are solid (and the French soldiers were) but your military high command will be worse than useless - then relying on fixed fortifications is actually the best possible national strategy. Your good soldiers can hold out for a while in the fortifications, taking (mostly) not-too-horrible casualties, without needing any orders from or action by your brain-dead high command.