From my admittedly not very knowledgeable perspective: Lack of user-friendliness, lack of good looks out of the box, lack of marketing did in the French bicycle industry.
With Campy, you order a group, open the boxes and bolt a bunch of shiny parts onto your (racing) bike. People recognize the stuff: "Oooh - just like Merckx' bike," giving you the valuable status factor.
With the French, you have to select and order a bunch of parts from a bunch of manufacturers (the short-lived Spidel effort nonwithstanding), and then often the work only starts!
A Mafac brake often looks quite unfinished in the box. A "constructeur" would braze the pivots onto the frame, polish the arms, and get a great brake.
Setting up a Cyclo derailleur is a nightmare - no customer would even want to pay even minimum wage for the amount of work. The Campy Gran Sport was easy: Bolt it on, pull the cable through the slot, tighten the bolt, done. Revolutionary! Which would a bike dealer prefer?
It appears that the French component makers often saw themselves as suppliers of half-finished material for constructeurs, who would make them into a finished product. On a Singer randonneur bike, it appears that about 1/4 of the total cost is for assembly and modification of various parts!
Campy's edge was the service-oriented approach - they made it easy for buyers/dealers to spec Campy. (Is it true that Stronglight headsets used to come without balls? I think so, but am not sure!)
Of course, Shimano took it one step further (Total integration - you cannot substitute, whereas with Campy NR, you could), and almost did Campy in! I am glad they recovered to their current strength.
Jan Heine, Seattle (who thinks doesn't believe that the best products prevail in the marketplace - Saab was bought by GM: Does that make GM's cars better than Saab's?)