Because there isn't enough of "us" to topple the web economy. Once a critical mass is reached, we'll see a (slow) mass extinction in the open web as we know it. Then a bunch of new business models will fill the niche.
Disclosure: I'm a Googler. Not sure how that affects my fatalism here.
Not sure what you would describe as "the open web", but from my perspective, the "open web" died with the hypercommercialisation of the web. Nowadays everywhere you look there are walled gardens, if they aren't walled gardens they are honey traps to lure you to divulge private data.
I think Google is working off and promoting a peculiar definition of "open web", which is an ecosystem of a) commercial actors, and b) resources (individuals) to be exploited by said commercial actors. The "openness" of that web is focused mostly of making it easier for the commercial actors to make money off exploiting resources. Efficient and unencumbered exchange of information or culture doesn't even enter the picture.
That's not the impression I got. Note that Google does not need the hypercommercialization to earn money. The moment you allowed your site to be indexed, Google earned its cut.
I'm not sure that really answers the question, though. My point was that only those with enough technical know-how get to choose to remain private; shouldn't everyone be able to choose as to whether they believe free stuff is a good trade for their privacy?
Also, why do we assume that the choice is between the status quo and the total collapse of the internet ecosystem? That there's no way for digital advertising to generate a profit without gobbling up ever greater amounts of our personal data?
Disclosure: I'm a Googler. Not sure how that affects my fatalism here.