Why can't USA universities evaluate international students?
Most students at US universities come from the USA, so it follows that their admissions procedures for international applicants will follow their general admissions procedures which are designed for US applicants. Unlike the other three countries you mention, the US doesnt have a national system of external evaluation for high school level students. So the universities have to work it out from yourselves. If they are doing that for the 90% of their applicants who are domestic, they are not going to put in a custom sub-system for the 10% or so of applicants who come from other systems.