Another military reason is that France did not add a sufficient counter attack force, something we call a "force de réserve" in case of a massive German breakthrough.
Obviously, that breakthrough happened in Belgium and some panzers / motorized divisions were able to flank the French army.
-with no "pure Armor" divisions, the French force was unable to oppose the Germans a strong defense, in spite of some minor successes.
-without any counter-attack force, the French army was unable to attack the German exposed flanks, to their big surprise as well, which allow the Germans to reinforce their breach for days before any reactions (which was too late) and trap the French army between them and the sea
The French army was basically egal to the German one : same amount of armoured vehicles and airplanes, but their philosophies of war were really different : blitzkrieg on one side, with large groups of armoured and aircraft used as a primary attack force, and defense on the other side with armoured and aircraft used as a defense to artillery and infantry
Those two tactics were partially influenced by the countries histories, demographies and abilities : France knew that she could use her colonial empire to sustain a long war and could afford to be passive. Germans knew the first blow needed to be the good one, and gambled everything on their speed and firepower
Overall, France surrendered for too many reasons to expose but some of them are :
-a trapped army, or what remains of it with a broken chain of command and structure
-the loss of any line of defense and the inability to create a new one in time : every "line" created after the invasion was reached by the panzer before the construction even began
-millions of people on the roads, with spreading rumours : did the USA entered into war ? Did Russia invaded them ? Did Hitler suicides himself ? Are the Germans slaughtering every soul on the exile road ? Those rumors are forgotten but we're like a poison on the road, and the French people lost his soul heading south
-people thoughts that Petain was just the shield, and accepting the defeat would allow France to continue the fight with its empire
-just imagine : your country has been military speaking outmatched like never before. In 3 weeks, 8 millions of people are on the road, the government is in exile, nobody wants to really fight after a long year waiting for the German attack, an old marechal, the hero of Verdun, offers to sacrifice himself and to sign an armistice
What would you do ?