"Although I can't understand the people who want to learn from videos."
I think the appeal must be the very low rate of information transmission. Watching someone typing slowly onto the screen, while saying out loud what they're typing, under the guise of presenting a "tutorial" on how to fetch input from the keyboard ("tutorial" being a very grand word for a slowly presented code listing) is something anyone can keep up with (although probably shouldn't bother).
That said, compare those to things like Casey Muratori who manages to push information at a higher rate doing essentially the same thing, except that he isn't just reading out loud what he's typing. Again, the information density and transmission rate thereof cannot begin to compare to a book, but there is something of a range to be found.
Straying from the topic, I've come around to the conclusion that there are a lot of people who want to be able to do things, but really don't know how to learn. To take on large amounts of new information, to think with it and ally it to what you already know and to adapt it to your purposes, and to do this for an extended time, is a skill like any other; it must be acquired, and exercised. If you don't know how to learn, if you aren't practised in it, a decent textbook might be simply unassailable for you and all you can do is inefficiently monkey-see-monkey-do your way around SO until eventually you've put together enough pieces to start actually building your own understanding.
So I suppose I've come to a second answer to the question; before SO, you either didn't learn at all, or you learned with an efficiency that must seem blisteringly powerful to some kid trying to bootstrap himself by trying to find the answer to "Why does it break when I try to store a string in a single char?" without even knowing that's the question to ask.