I think it's just like that because that's just how it has been traditionally done in America. Their toilets are also a different shape - much wider, lower and shallower. And urinals always have flush handles.
I haven't actually seen many newer urinals with flush handles. Pretty much anywhere with a recent install is sensor based. There's plenty of old equipment around, of course.
Toilets are more hit or miss, though I'd hazard a guess that the majority of new installs are also all motion / sensor based. I can't speak to the bowl differences, though I'd suspect they're due to water efficiency, disabilities compliance and / or our heftier girth.
Google image search gives good examples:
https://www.google.com/search?q=us+toilet+stall+gaps&tbm=isc...
The vertical gap between the floor and where the cubicle wall starts is huge. Like, knee height. So weird.
I mean, imagine mopping one of those rooms. Bet you'd immediately be glad the partitions didn't reach the floor.
source: i am a cleaner.