You don't have to turn it off during an airliner takeoff because the only system it's going to interfere with is the one in your brain. You don't have to wait for it to boot, and it never crashes. You don't have to rewind it. To find your place in it, it takes a half second to turn to the bookmarked page. You can gain something from the right book with 30 seconds of concerted study before you go into an important meeting.
Books are hospitable to an enormous range of content.
They do everything from office etiquette to SQL programming. There are no real alternatives to books for complex subjects or for subjects that involve mountains of content. Given all of print's virtues, it's hard to imagine how its utility is ever going to be surpassed. That also goes for its cost. Books are ludicrously cheap by comparison to most other training media, unless you buy huge quantities of them.