Sadly, schools are broken
I'm most knowledgable about the US market but over there the teacher shortage generally means that you end up with teachers having to do quite a lot of work outside of their own subjects, such as — for example — PE teachers teaching maths. Because they don't know the topic all that well, they're quite dependant on the textbook. Meanwhile, states require that textbooks be certified at the state level before schools are permitted to purchase them.
As a result web sites are generally out as a teaching tool because the subject-hopping teachers prefer to trust what the state has explicitly approved and the subject-native teachers can do without the liability of turning away from the specified materials.
The conservative approach that goes into textbooks prior to submission to state bodies therefore leads to children carrying around huge, heavy books with words that were fixed in stone a long time previous.
Forget the Apple angle; any move to electronic materials — which are less regulated at present and needn't carry the same heft or price — will be a great advancement.