I don't know why it's such a big deal in the U.S., but as you say, it's standard practice in most of the world. I'll go further and say that it's for natural humans.

Can you imagine a scenario in pre-history (when we could first call ourselves homo-sapiens) when the parents would be like "okay, you can fuck off a sleep in the corner now"? There's a reason children scream like that when you try it. Listen to the difference between that crying, and crying when there's just generally something a bit wrong like they're hungry. You can rationalise it all you like, but you're traumatising the child.

Having said all that, I did _not_ find it easier, but incredibly difficult.