Many subjects don't NEED "new and updated" textbooks. Honestly, has primary & secondary math changed in 50 years? Yet new textbooks are issued every 2-3 years. Science changes, but even that is slow compared to a high school student's career - doctorate-level ground-breaking research takes 30 years to filter down to the high school level.
If you're looking at e-books, history and science texts could be simply added on to instead of completely replaced. The publishers probably won't let that happen, though. Big money in textbook publishing.