On the internet - no one knows you are a dog

The adage that if you are surfing on the internet no one know you are a dog, is of, needless to say, 

dubious veracity

Although modern online media allows a high level of  anonymity, I mean you can set up alternate identities, 

however to counter this there are new forms of identification, documentation and tracking, this threatens

normal intuitions about identity. 

So what is the drive or the force behind the 'big brother' type identification, documentation and tracking?

How about Capitalism? And the desire to sell you something.