As long as things worked on these assumptions, this was working reasonably. However along came the e-commerce revolution. People needed traffic to their sites. If you have a large enough number coming to your site, a certain percentage of them would become buyers of your products. Now, if visitors cannot find you in the millions of search results, you remain the store on the main street of some obscure town-the internet equivalent. You have to get on to the first page if not the number one position!
Along came the SEO experts and discovered the above among other things. I am sure they work. But one direct consequence is that a lot of content on the net is simply useless. They are aimed at generating these keyword densities and the backlinks. The actual content could actually be meaningless. It' gotten so bad, you'll find sites easily which has parts of a page simply repeating the keywords over and over again. Meaning of "ad nauseam" hits you straight! Generating backlings has taken over the comments on forums, blogs and networking sites. There only aim is to create a link back to the target site. What the comments say is irrelevant.
People have started realising this, I guess. There is a momentum building slowly about quality content. Just the stirrings now. Hopefully, things will work out.