When you have all these things together you are going out of speed that is accelerated. You're going faster than you could go just working on all of these aspects by yourself. It's a speed that is practically impossible for the average person to reach.
How can the average person who has no knowledge of these tools and tactics, be expected to learn about writing, learn about publishing, learn about promoting, and somehow find the social networks that they need in order to get promotion and get off the ground?
It's extremely rare as evidenced by the very low number of people who actually get it done.
Facts are these - writing your book is not what makes your book sell. There are a lot of books that have been written and are pretty darn good but don't sell.
You already know how to write a book. You know how to structure it you know how to come up with great ideas, you probably know how to do a little research, and maybe you've even designed one or two covers along the way.
It's extremely disheartening and depressing to work so hard on your book, only to find that the real struggle isn't the time that you spend writing...
The real struggle is the struggle to turn, what you write into something that sells.