I would assume that if Google is paying 10$/hour for humans to rank content, someone else is paying 11$/hour to fool it with a human generating content, clicks, etc.

Additionally, people writing bots learn just like Google learns, and start generating what appears to be legitimate interactions. Same algorithms that fit to critique between 'bot' and 'non-bot' class can be used to create bots that fall into the 'non-bot' category.

It's a losing battle - but what we get is better than we would get if they collected less data.