One of the problems here is the effective monoculture. If there were multiple search engines in use with different ranking algorithms and different search stra

One of the problems here is the effective monoculture. If there were multiple search engines in use with different ranking algorithms and different search strategies, then "SEO" would be difficult to impossible to achieve because optimising would one search engine would likely be a pessimisation for the others. We don't just need one competitor, we need many. And they can't just be copycats, they need to do their own thing, and that might well make the cost:benefit of SEO unviable.