I can't speak for Americans in general, just the breeds of the Americas vs the European and Arabic type sheep. With the standard breeds in Europe it was acceptable to not cull bad behavior or sickly animals. The are highly prone to predation. A shepherd stayed with them, tending to them. As a blanket statement when talking about the breeds as a whole they are not very hardy, prone to illness, prone to parasites and it's very common for the ewes to reject lambs. These undesirable traits were inbred over centuries. Now that the economy requires most to work a full time job it creates a burden to inoculate, worm and bottle feed all hours of the day and night.
With the breeds of the Americas a blanket statement would be they are pretty well parasite resistant. They are very hardy not prone to sickness. They very rarely reject lambs. Generally they can protect themselves from predators. Blanket statements are highly unfair, however many truths ring true for the respective breeds and their origins. Most people in America don't have the time to care for lambs since most households have both parents working and children can't be expected to get up at 2am to feed the lambs. But they make the mistake of getting a breed that has been babied for centuries and they have to fulfill that roll. The only way to turn it around is culling or get rid of the breed and get one of the more self supportive breeds common to the Americas.
By the way it's not my intention to be cross, or a know it all. It's just one of those aspects that people don't think to research before they jump in and it turns into a very overwhelming negative experience for them. I raise mouflon (wild European hair sheep breed), american blackbelly and bighorn. I have had 2 ewes in 20 some years that did not allow the lamb to nurse. They were introduced to another with a baby and accepted. The ewes were tagged and butchered later. I have no need for an animal that's not sustainable as I have a farm to run, a full time job and smaller jobs to worry with. For me it boils down to time. Yet the traditional high maintenance breeds would not be high maintenance today had the shepherd's been of the mindset of improving breed health, parasite resistance, lambing and predator resistance instead of greed to have as much fleece and meat as possible for market.