> Why is this so prevalent and people see it as a viable strategy instead of focusing on product and customers?

Because there is a market for easy money courses. As long as there is a demand and easy to do then people will work to supply that demand.

For example, imagine if there was just a single person making these "make money doing X" books, he would get very rich. People would copy him to also get rich, and then enough people enter until it is no longer easy to become rich making such books. So just standard capitalism.