[ChuckMcM]

I think this tells a more nuanced story than just "clicks aren't worth it."

Search advertising has been very lucrative for a lot of people, this was especially true when there were few contested keywords and the cost to land on a page was low by comparison.

However, if you look at Google's results over time, they grew spectacularly as they added advertisers and their price per placement was growing. Then the growth of advertisers slowed because there are only so many of them in the world, and in their latest results you can see that the price per click has stabilized (and declined slightly) as well. Both of those point to a maturing of the search advertising market.

My guess, and it's only a guess, is that Google's revenue from search ads has peaked. (Peak Ads anyone :-)) and going forward the dynamics of that market will be a lot more subtle. More complex advertising packages will be created that increase the total number of pages where ads are shown but do so in a way that spreads cost around (like discounting a front page add if enough "page 3" ads are bought at the top of that page).