clairobscur, allow me to try to explain my view of the matter:
From what I recall of my time in Paris, there really wasn’t a difference between a cafe and a resturant. In the US there is a large difference. Not simply in menu, nor atmosphere, but targetted clientele, too.
In Paris, what I saw was that most cafe had was 50%, or more, of their floor dedicated to small one to two person tables. These could, usually be combined for larger parties, when necessary, but they expected much of their business to be coming from the single diner. In the US, that sort of floor plan is going to be used only by what are called cafes: places that cater as much as possible to the idea of a European afternoon sitting over one’s after meal coffee, and reading the paper or a book, or for long talks with a single other person. Most resturants, proper, however will have a floor plans with maybe 10-15% of the floor dedicated to such small tables. So, when the singleton comes in and insists on sitting in the dining area, (instead of the bar/lounge) there’s already a loss of 75% of the potential revenue for that particular section of floor space, because there’s only one person ordering there.
Then there’s the differences in how larger parties order while lingering after a meal, compared to what I, for example, will do when I’m sitting after a meal reading. I’ll sit there, indulging in free soda refills, and may, if I stay long enough, decide to add a dessert. Usually for the same time that another whole party could have used the same space. As I said before, this isn’t an issue when the eatery is off it’s peak hours, but during that peak time (which in the US is a 90 minute to two hour window) it’s very much a matter of floor space equals money. The larger party, however, will usually be continuing to make orders from the bar, for alcoholic drinks or bottles of wine. And while a singleton diner would have to look at something more on the menu with the thought: Can I eat the whole thing by myself? The group, however, is far more likely to order a series of small after dinner snacks to keep up with the drinks, because they’re ordering to share throughout a group.
It’s still a revenue loss for the eatery at peak hours (And I have suspicions that most eateries actively work to try to seat larger parties latter in the peak hour time, so that there’s no pressure to push them out the doors.) but far, far less of one than a singleton diner would show.
And again, the push to push people out of tables is not a feature of the entire time the eatery is open, just during the peak hours: 11:30 AM to 1:00 PM for the lunch crowd, and 6:00 PM to about 8:00 PM for the dinner crowd. Outside of those hours, the eateries aren’t going to care about having a singleton sitting there reading, what-have-you: there’s no sense that they could get more customers in, if only the one(s) sitting would just leave.