How many secondary school mathematics books have been written since, say 1900 ? I don't know but I am sure there are many. I wonder what the authors of these books had in mind when they wrote these books. Were it the results of students? Orders of their (publisher-)employers? Or plain greed? Mathematics does not change because time passes. And what was the role of the department of education? How are they linked to the publishing industry in your country?
I am sure that everyone agrees that Gauss and Riemann received an excellent secondary school education, and neither were born in a rich family, to the contrary in fact. They had genius minds of course, but mathematics was flourishing in these days. What books did they study, I wonder? I am not sure, but for geometry they must have studied the works of Euclid, and for algebra and number theory they likely studied works of Euler.
Almost everything high school students have to learn for algebra is in Euler's books, really. All these books need is a modern e-book look and feel and you are done. And Euler starts really at the beginning, it's all there. A 10 year old can start studying maths from one of Euler's books. We don't need more books of the same. Do we? Have I mentioned that Euler's books are free? Does that ring a bell?
Euler's Elements of Algebra.