They're not, it's an illusion.
My older sibling went to HS in Eastern Europe and kept the textbooks, because my family had this same reverence towards math over there. I went to HS in Canada and in grade 12 when I was doing Calculus I had a look at the old textbooks and they were the same thing. Different styles certainly, but the problem sets were basically interchange. In Algebra and Geometry, the Canadian books seemed to have much more emphasis on algebra, whereas the eastern european ones had much more emphasis on geometry.
I think the illusion comes from the different rates at which you're expected to pick things up. Grade 8 Canadian math was much easier, so I think the Canadian curriculum was backloaded - easier in the early grades and much harder in the later ones, whereas the eastern european one seemed much more even.
>Grade 8 Canadian math was much easier, so I think the Canadian curriculum was backloaded - easier in the early grades and much harder in the later ones, whereas the eastern european one seemed much more even.
This tracks with British Columbia's secondary school math curriculum. [1] For Grades 10-12, where the grades actually do determine whether you graduate, you're given off-ramps if you can't handle the more difficult math courses. (Workplace mathematics where you'll learn practical applications of math, Foundations of Mathematics where you do Pre-Calc 11 over 2 years instead of 1 for Liberal Arts/Trades programs, and Pre-Calc 12/Calculus 12 for STEM). From Grades K-9, everyone is largely kept at the same level and completing it is largely unconditional (if you're not doing well, they may give you an Individual Education Plan to help you catch up).
[1]: https://curriculum.gov.bc.ca/curriculum/mathematics