Louis XVI had really big hair. Probably for this reason, the decadent French aristocracy specialized in greyhounds. Pugs were the favorite of the ladies (supposedly in more ways than one: the term "lapdog" had special meaning for seventeenth-century pornographers, and during the Revolution pugs were burned alive).
But then as now, many French had little fuzzy mutts known as "caniches." Perhaps it was this dog's modest unobtrusiveness that allowed it to survive the Revolution unscathed. During the Third Republic (a.k.a. belle epoque, 1870-1914, a period of rampant opulence), its capacity to form enormous topiary massifs of stiff, swaying hair was finally recognized and fully exploited.
Elaborate functional rationalizations soon followed. The familiar "lion clip" began because a fully-furred retriever (see Myth #2 above) might soak up too much water and drown. Ankle pompoms served to keep the swimmer's ankles warm. (What about the tail pompom and topknot? Which parks in Paris allow duck-hunting? Why not hunt with spaniels like everybody else?)
The poodle's golden age came after World War II. This was another period of conspicuous extravagance in France. The extreme femininity of Dior's "New Look"wasp-waisted, gathered skirts sweeping the floorcalled for a feminine dog. (It is instructive to note that devotees of the butch, pragmatic Chanel line are usually pictured with fox terriers.) The poodle's springy walk and bouncy hair reflected the new youthfulness and energy of the 1950s super-housewife. The immaculately shaved and fluffed pet by her side confirmed her urbanity and sophistication even as it suggested her regression to the controlled sexual norms of the Third Republic.
Also, France has no "national dog."