I think it's true that they're filtering for people who value that opportunity, but I'll also note that those people fall into two important categories. First

I think it's true that they're filtering for people who value that opportunity, but I'll also note that those people fall into two important categories. First are those who want to work at Google itself. Second are those who want to have Google on their resume, and an extra bucket of money from being overpaid for a few years, as a way to jump-start whatever they do next (including startups). Google is glad to have these ambitious, slightly mercenary types pass through, making contributions while there and then seeding the rest of the industry with allies. If Google were just hiring the lifers their interview process would be even more rigorous but less burdensome and demeaning. They're deliberately selecting for ambition and determination as much as actual talent.