I have no inside information but I'd assume this has something to do with automation. They ask for your Google Account when you fill out the application and th

I have no inside information but I'd assume this has something to do with automation. They ask for your Google Account when you fill out the application and they said outright that they were looking for people who "live on the web". Since we know they keep all kinds of usage data about their users it's just a matter of matching an application to accounts with heavy usage and sending them out accordingly. All of which could be done by a computer.