They know that by not missing out the basic information, they will get a buyer for a long time.
Think about it for a moment, what don't you know and what would you buy to teach you that information.
Take scripts for a moment, I know nothing about programming. I don't want to buy a book which assumes I know programming languages, because that isn't going to help me at all. If I find a course or book which starts at the very beginning, then I am more likely to buy the next one in the series and the next.
Why do you think offline, there are book teaching different levels. Once you finish the basics you move to the intermediate and then to the advanced.
When someone says they want to learn, guess what you'll recommend, the books that helped you.
Just because you are not in the beginners stage, remember what it was like for you. Follow a course step by step and see why the marketer does that.
There is silver in watching what they do. But there is gold in understanding why they do things.