Did you ever see an optical illusion? Initially, you see only one image and you assume that is all there is. Then suddenly, a different image appears. One I remember is an old lady with a big nose (image below). When I looked at it a little longer it appeared to be a young woman with her head turned (or you may see it in opposite sequence). Voila! There is more here than first meets the eye.
Doesn’t that remind you of non-bookstore marketing? Initially, people see selling books only through bookstores. Then the moment comes when they say, “I see it. There is another way and that is selling to corporate buyers and through non-bookstore retailers.” That is when real book marketing begins, and sales start to happen.