Every French story about food or women has more than one version (cf. the invention of the
brassiere). Why, some of
my stories are suspect...
What really put restaurants over the top was a health-food fad of the Napoleonic era: bouillon. Seems as if one fashionable diet was based on drinking the liquid beef (or other meat) was cooked in. Since beef is boiled in water with lots of vegetables, the prevailing wisdom was that the water somehow took in all the nutrients of what it cooked, therefore drinking the soup was more nutritious than actually eating the meat....the perfect food. (No one thought of fiber back then...) Anyhow, the scheme was that you had to drink this liquid (for maximum results) every two hours. Since meals tended to be six hours apart, this meant that one had to take a cup of bouillon with you while gadding about town, or have someone cook it for you at an inn or traiteur. Well, traiteurs didn't have tables to eat things from (being something like a convenience store or Korean grocer) and inns had tables, but tended to have only set menus (kind of like staying at someone's house). So, where do you eat? At a restaurant!
Anyhow, restaurants had their ups and downs for more than a century before becoming an urban fixture. Napoleonic wannabees adored them, and you could see all kinds of men, women, and other creatures sitting at tiny tables sipping broth, eating ice cream, and such exotic drinks as soda water while gazing into each other's eyes. During the Bourbon Restoration, this became a somewhat declasse activity: only smart young men and prostitutes would dare to eat anywhere other than each others' homes. As the century went on, however, prostitution became a bit more, shall we say upscale, and the places became gradually more elaborate to set off the dazzling ladies of the evening who frequented them -- as well as the dishes and service, which necessitated a corresponding elaboration in kitchen organization. French cooking (especially with entrees) became modular: intead of cooking something in spices or in a distinct manner, meats were cooked without seasonings and sauced and garnished to make various varieties.
By the turn of the century, respectable women were seen more and more at such establishments, especially during the day, and by the First World War, the process was complete.