Real simple, no internet.
Ever try travelling and you need consult the online help and you don't have a connection? There ya go. Airplan, no connection. Train, no connection, sitting in the terminal, no connection. Your internet goes out, no connection. With local help you never have to worry about getting the documentation for a method or property.
You cannot assume that internet is 100% reliable. Cables get dug up by mistake and you could be out for hours or days without a connection. We are not at the point of where we have wired and wireless connections which we can switch seamlessly between.
I do have a fast wired connection, so it is not an issue of speed. And yes, when the internet does go down when you are your desk, panic sets in immediately because you know you do not have the ability to search for answers. With local help files, you are not totally in the dark. They may not fully answer your questions and you will need stackoverflow.com to come to the rescue as some point, but at least you can remain somewhat productive.