The French have absurdly lavish social welfare policies, particularly for the middle class and for workers. Opening France to more economic competition threatens their cushy perks. (I knew a French businessman who wanted to fire a lousy truck driver who kept missing work. He had to make an appointment with government bureaucrats six weeks in advance in order to get permission to fire his own employee.)
This points to one of the great ironies of globalization: It imposes a regression to the global mean. Various commentators have marveled at the fact that Britain and France think the EU Constitution means opposite things. The Brits don't like it because they fear it will bring Euro-socialism, while the French fear it will move France in the laissez-faire direction. Many have attributed this to voter confusion over what the constitution actually says. Why else would the Brits think it's a socialist tract while the French are convinced it's a plan for economic liberalization?
While it's true that the proposed constitution reads like a Xerox machine repair manual, the voters aren't that confused. France's bourgeois welfare state would have to be unraveled under the new regime, while comparatively free-market Britain would find its economy pulled toward greater statism.
Add the fact that the document itself is impenetrable and you can hardly blame voters for erring on the side of caution. You don't roll the dice when you might potentially be voting away your sovereignty and lifestyle. For the record, though, the constitution is no free-market tract - if Adam Smith were alive, he'd spontaneously burst into flames if he read it.
Of course, there were other reasons the constitution failed so spectacularly, including: 1) The French political system is scandalously undemocratic, and the French people felt they hadn't been consulted. 2) This may have been the last chance voters had to express their fears of Turkey joining the EU. 3) Chirac and Schroeder are unpopular fossils. 4) Ours is a just and decent God.
In any case, America and Europe have a wonderful opportunity to rework this project along lines that are in Europe's interests and ours. Let's just hope that French and German egos can handle Uncle Sam coming to the rescue - again.