It's not just a curriculum issue. There are fundamental differences between math education in the US and math education elsewhere, which is where the curriculum issue comes from.

As part of the 1998 TIMSS, a couple hundred videos were made of math teaching in the US, Germany, and Japan. James W. Stigler and James Hiebert then wrote a book, "The Teaching Gap: Best Ideas from the World's Teachers for Improving Education in the Classroom", on the content of these videos. They observed:

"When we watched a lesson from another country, we suddenly saw something different. Now we were struck by the similarity among the U.S. lessons and by how different they were from the other country’s lesson. When we watched a Japanese lesson, for example, we noticed that the teacher presents a problem to the students without first demonstrating how to solve the problem. We realized that U.S. teachers almost never do this, and now we saw that a feature we hardly noticed before is perhaps one of the most important features of U.S. lessons - that the teacher almost always demonstrates a procedure for solving problems before assigning them to students. This is the value of cross-cultural comparisons."

"For example, presenting a problem in Germany sets stage for a rather long development of a solution procedure, a whole-class activity, guided by the teacher. In Japan, presenting a problem sets the stage for students to work, individually or in groups, on developing solution procedures. In the United States, presenting a problem is the context for demonstrating a procedure and sets the stage for students practicing the procedure."

Or, as a review of the book on Amazon summarizes:

"In Japan, mathematics teaching is a method that aims to develop students' understanding of mathematical relationships and properties. This system of mathematical knowledge is taught to children in lessons that are highly coherent, hierarchically linear, and based on teachers' own research of what lessons promote student learning. Further, these lessons typically involve "structured problem-solving," where math concepts are induced from challenging problems, where these concepts are concretized through well-considered examples, and where mathematical relationships are proven as following necessarily from given premises.

"In contrast, mathematics teaching in the U.S. seeks to train students in mathematical procedures. These procedures are taught to students by demonstrating one correct procedure for solving an easy problem, and then students are asked to imitate that procedure for many highly similar problems. More often than not, the lessons for imparting these skills are incoherent--with many non-mathematical discursions and interruptions. Further, lessons almost never involve math inductions and proofs; rather, teachers state math relationships explicitly and immediately tell students how the relationship should be used to solve simple problems. Last, lessons are developed by education researchers not only without the collaboration of teachers, but specifically so that the lessons are 'teacher-proof'."

That's the difference: other countries teach problem solving and (deep) understanding. The US teaches simple, repeatable procedures. That's what then becomes "teaching to the test".