I don't understand the distinction you're trying to make. I think what's being proposed is that the more undiscovered markets get discovered, the fewer undiscovered markets are left, and the more difficult they are to discover. Pagerank was a good idea that worked.

And back at the time, before Google Search, many many related markets didn't, couldn't, yet exist. And, back then, I'd think PageRank could count as one of the few and difficult thing to discover.

I think "low hanging fruit" makes it sound too easy :- )

Then you missed the point. It doesn't matter whether PageRank was something trivial any grad student could come up with or if it was on the level of Einstein's General Relativity in difficulty. The point is that it was one basic idea.

Today if you want to dethrone Google you need to overcome the enormous amount of engineering that has gone into Google Search and Maps. You can't do that by just "discovering" something as a grad student. It's going to take thousands (or millions) of engineering hours to achieve.

That is what it means for the low-hanging fruit to be gone. It's like the difference between discovering electricity, as we all know took quite a while but was achieved by a small number of scientists and inventors over a period of a couple centuries, and trying to compete against the modern-day electrical distribution network on your own, which is essentially impossible without some kind of Star Trek alien galactic empire level technology.

The big guys at that time were blinded by their own success, Google wanted users to do their search and leave the site which was completely opposite to what the Yahoo's of that day wanted to do, they wanted users to hang out on their portal.