For many reasons. First, because they can, and nobody will ever have a chance to know about it. It's not like people are going to whistleblow: from the comments

For many reasons. First, because they can, and nobody will ever have a chance to know about it. It's not like people are going to whistleblow: from the comments of many Googlers here I understood they (or a reasonably large number of them) really don't see tracking as ethically wrong. That's of course very good for their mental health, but less so for the privacy of most Internet users.