> point of textbooks is to educate people on some topic so making them as easy as possible seems like the correct choice

It is not possible to “educate” someone about mathematics or math-heavy technical fields without convincing them to put in some serious time and effort thinking deeply about hard problems.

Many US high school (and even undergraduate) textbooks are more or less analogous to taking a look-out-from-the-bus tour of rock climbing sites, or maybe like teaching an advanced wood shop class by making students assemble IKEA furniture.

Textbooks should be exciting and fun, but “as easy as possible” is a terrible goal.