Doesn't fit in a rail car, at least not when paired with a walkway, and a counter/bar, and a kitchen?

You can fit at least 6 in one of those booths. Get closer with your friends! You can also play musical chairs and lean over the divider (or could before covid)

Their absence supports that it's not an omnipresent American pattern after all.

Couple of things.

First, the patrons never put the tables and chairs back where they're supposed to be (even if they try, they get it wrong), so the minimum-wage waitress/busboy is stuck with the job of rearranging furniture, and cleaning up the floors. This is one reason that large groups get the "mandatory gratuity" treatment.

Turnover: every restaurant needs to turn over tables on the regular. If a large group is sort of lingering even after being decimated, and the diner can't reclaim those 4-tops for another party, that's potential lost revenue.

[Hmm, is that how "The Four Tops" got their name?]

Wait staff are often assigned "stations" based on a group of table numbers, so if you shove together enough tables for 12 patrons, you may have a conflict of 2-3 waitresses, but only one "main" can be allocated.

Any table or chair that can be lifted or moved by a patron becomes a potential melee weapon. Diners are occupied by rough crowds and after-club drunks who are trying to sober up. This is also why you're lucky to get a butter knife with your sirloin.

Booths feel more comfy, and offer a better feeling of privacy than tables. A table's more flexible if you have a family and toddlers, a wheelchair, or something, but booths are for lovers to cuddle.