It’s easy to make a decent small search engine: nobody is working to game your algorithm. Vastly harder to do this as you scale to google size and popularity.
That's a great argument for a more diverse set of search competitors, especially with their own index. Imagine if we had 10 viable search engines rather than just the 1 (or 1.5) we currently have. With multiple ranking algorithms a SEO-bait site would work on one or two but unlikely on all 10.
