they are looking for numbers, pure and simple. While
you may not buy anything, lots of people do.
Think of it this way, if 10 million people see an ad on a major website and only 1% of those people actually buy something spending an average of $5, that's still over $500,000...now think of youtube videos that get 300, 400, 500+ million views.
This makes for some amazing reading:
"I'm feeling lucky" button costs Google $110 million per year