Today, I suspect the benefit of having said data is probably unknown. This data is probably only valuable in aggregate to determine trends.
Showing you a random advertisement vs an advertisement based on the page info vs an advertisement with your data included. I suspect an advertisement based on the page info is 90+% of the value.
That being said, they can't truly pay you meaningful amounts for your data and answer to their shareholders. That's why it's not really done yet.
Plus, they dont' need to in many cases. The whole internet is designed to collect all this data from you, without your consent being necessary.