and I would amend the whole V8 vs tiny European engine thing---its more modern I'd say, when highways were being put in during the 50s and 60s, the V8 was common, while in Europe, cars and trucks traditionally were smaller with smaller engines, so the switchback thing just made sense for the vehicles. Whereas mom and pop in their Chevy could just V8 themselves easily up long steeper hills.
my theory anyway
I was curious about this and the tradition to build switchbacks in Europe seems to predate automobiles. Some of the mountain roads may be as old as the roman empire but some of the still in use roads were built in the early 1800's when cars weren't really a thing.
One reason for the switchbacks especially in the alps may be due to gradients which would be quite impossible to manage with any vehicle if the roads were built just straight on. You do see the straight over the mountain roads in other places though. The ardennes have pretty brutal gradients (not nearly as bad as the alps though) and no switchbacks. Not fun with a bicycle.
Personally I feel the switchbacks may be safer overall as they limit speeds and allow for constant engine braking. They can be difficult with heavy traffic though.