Why do US coaches have open seating vs. compartments?

Why do US railroads operate coaches with open seating (i.e., all of the seats are together in one big room, without dividers), while European railroads have often had coaches divided into small compartments?

If you're in a US coach with one loud person, you can't get away from the noise. In a traditional European coach, if there's one loud person, the person is confined to one small compartment, so fewer people are bothered.

I know that modern European railroads are moving away from compartments; I wonder why.

Thoughts?

America isn't hung up over class as much as Europeans are. Every man and woman is equal, therefore there is no need to have separate corridors leading to different restrooms in the same car. Americans also seem to prefer riding in forward facing seats, which open cars easily accomplish where many smaller compartments in cars can't accomplish at all. Besides these nuisances, I believe it's easier to cram more seats into a open car than one with compartments and that's why Europeans have also adopted open coaches.
British Mk2 corridor first coach capacity = 7 compartments with 6 seats = 42
British Mk2 open second coach capacity (2+1) = 48
British Mk2 tourist open second coach capacity (2+2) = 64
I don't believe British Rail made any compartment Mk3 or Mk4 coaches. Obviously the higher seating capacity on the same size chassis makes them more efficient.

FYI,
Amtrak standard Amfleet I capacity (short distance) = 84
Amtrak standard Amfleet I capacity (long distance, considered business class today) = 60
Amtrak standard Amfleet II capacity (long distance) = 59

The question to ask is why did the Europe adopt compartment coaches at first, and why America adopt open coach all along? The surprising answers has more to do with what they were copying or what they were targeting as competition. Per Wiki:
Europe trains were targeting horse driven stage coaches, even using the same coaches on trains with new wheels. America trains were targeting steam riverboats with center aisles along their entire length.

While I partially agree with railroads targeting steamboats, electricron, I think it's more your first statement about Americans being class-conscious in the opposite way as Europeans. Even today, Americans prize politicians that appeal to the "common man," even as they grouse about the guy in seat 14B who just won't shut up about his weekend in Atlantic City or the lady in 24C who has her music up too high. Same with how Americans often prefer to complain about traffic jams on freeways, rather than pay a toll to use a fast lane.

And the inefficiency of closed compartments is pretty staggering compared to open seating too.

Three other possibilities:
1) The American design was cheaper to build without all those doors along each side;
2) European stations have always been abundantly equipped with signs, while in America it was essential for a trainman to walk through the cars announcing the next station, which might have one sign on each end of the building, perpendicular to the track, and possibly not illuminated at night;
3) In Europe, tickets have traditionally been punched at the platform barrier at origin and collected at the barrier at destination and examined once, if at all, en route (imagine ticket barriers at every station on the Burlington or C&NW across Iowa); in Britain early in the 20th century some railways had ticket platforms just outside a metropolitan area at which all trains would stop prior to arrival at the main station for all tickets to be examined by station staff, compartment by compartment, before the train could proceed to the main station. In America tickets have always been punched and collected, and hat checks issued, while en route.