Google's motivation, in all that it does, is to index your data an sell you to advertisers. Advertisers are the customers, and you are the product. Android, Gmail, the search engine, Google Drive, Google+, and so on--they all exist solely to index people's data and serve them ads. 96% of Google's revenue comes from advertising. It is their core business.
In fact, that's not actually bad in and of itself, up to the point where it crosses into creepy territory, like in this case. Just by uploading your personal files, you are licensing them to Google to do whatever they want with them. And not just Google--note the parenthetical "(and those we work with)". So you don't even know who is going to be using your personal data. I mean, these policies actually give Google and other strangers the right to publicly display and distribute your files. One wonders if that absolves them from any consequences from security intrusions too, since a hacker getting hold of your files that would count as publicly distributing them, even if accidentally.
I've never bought into the image of benevolence Google always presents to the public, and that's cost me Slashdot karma over the years, but I don't care. It will be very interesting to see who defends this. It would be difficult not to see them as sellouts of themselves, all too happy to trash their own privacy rights, eager to please the advertising megacorp and defend them from attack. Wake up!