One step at a time
Other countries around the world will have a basic math class for their students, which covers everything from algebra to geometry. In America, there are different classes in math or another subject; they like to split it up into different parts. It is very common for there to be Algebra 1 class, then Algebra 2, and so forth.
This is a very common practice in American schools, as some students might find it to be overwhelming to learn different topics all within one math class. We’re not actually sure why subjects are split up into segments when in other parts of the world it is a standard practice to learn math, science, and everything together.