There were various reasons for a swift French capitulation during WW2, none of them are satisfying to the 'meme community' however (by which this event is most well-known). This is largely because it may seem funny to poke fun at French incompetence, yet all the evidence from the time suggests otherwise.

To understand the issue at hand, we must first understand why the Nazis had the upperhand. Hitler and his generals are largely thought to have developed their 'short war' (Blitzkrieg - literally 'Lightning war') strategy indepedent of outer influences. This was a new form of strategy and hadn't really been used in a war before because the technology necessary for such a tactic was not available. In particular, the introduction of the 'panzer' tank was essential to this strategy. The new strategy meant very large countries (such as Poland) could be fully occupied within a few weeks. This undoubtedly damaged the French war effort, the people feared such a quick and brutal occupation.

A second factor is likely to be the fact that there was little support for another long war - this time with some Frenchmen under iron-fist fascist rule (likely closer to that which Italy experienced rather than Germany). War support was at an all-time low, and many Frenchmen felt only a few possibilities would occur. Firstly, they would be controlled as a Nazi puppet and then released after the war, or secondly they would be released as a free state under annexation of a few territories (Alsace-Lorraine in particular). Neither of these were particularly unpopular in France, and it was felt that sending men to die against an already fierce war machine was useless when they were so unmatched.

This is not to mention the plans the Allies already had to retreat to colonial France in the event of occupation. There was little expectation that the UK could ever be captured, and a tactical withdrawal to Africa was deemed more sensible than the alternative of fighting in France. Some historians have suggested it was common knowledge among the German leadership - probably even Hitler himself - that the Polish war was intended to be separate from the French war, these historians also note that Hitler believed such a war would have to wait until 1943. He did not anticipate an Allied defence of Poland. The economic statistics coming out of Germany were impressive however, and the French were probably fairly scared of this 'economic miracle'. Not to mention the 'ghost rearmament' that came with Schacht's use of MEFO bills.

It is important to note however, that Hitler had respect for the French. He deemed them a superior race in their own right, and even deemed some in Northern France to be frankly Germanic. This meant the oppression faced was far less harsh - French collaborators were willing to hand over Alsace-Lorraine after the war in return for a relatively free - but fascist - state.

In conclusion, it is impossible to envision a world where France could've simultaneously held the extended Maginot (including Belgium) and the Italian border without seriously overstretching themselves. The likely scenario is that a tactical withdrawal to Africa was envisioned as a popular move where they could properly develop and prepare an army (especially given the rich resource areas in Africa) as well as save lives (the Nazis did not oppress the French as much as they did other groups). It was largely seen that a French surrender would mean more preferential treatment (which it did) and therefore fighting a lost war was seen as pointless. The Allies probably already knew a Soviet war would eventually take place, and planned to take advantage with an invasion, though plans would not come till later in the war.