The bigger question may be why do we even still have "textbooks," at least in their traditional form? Are textbooks the optimal way to learn given all the technology we have today? I'm sure there are quite a few start-ups working on this problem.
Studies have shown that text is not the ideal format for novices to learn a subject for the first time.
I'm a co-founder at https://www.clutchprep.com and that's what we're tackling. Students go to 300+ student classrooms, don't learn much and then have to rely on a $250 textbook to teach themselves (doesn't work well for most). It's a broken system.
Edit: fixed the link