In my opinion, it's so they can track consumer's habits so they can market more stuff to you. They also do it so they can sell the data they collect on you to o

In my opinion, it's so they can track consumer's habits so they can market more stuff to you. They also do it so they can sell the data they collect on you to other companies who want the same thing. Round and round we go, until all of Silicon Valley knows what you buy, browse, and are likely to want. But maybe that's just me being cynical.