Because airlines and pilots operating within the U.S. are subject to significantly more safety restrictions and regulations than much of the rest of the world.

Put simply, pilots are required to undergo more training, observe best practices in CRM, and have strict requirements on how much rest is required between flights. Planes are better maintained and inspected.

I’m sure there are other countries that do a good job here, but in general America is significantly more strict about these things than much of the rest of the world.