User tracking isn’t done to send you spam, it’s done to make real time ad auctions. When you go to a website where all the content loads, and 10-15 sec later all the ads load, what’s real time auctions.
This is why they do the tracking, they need to know which user is accessing which ad space, this is what allows them to make the auction.
When you access the website, Google will give your profile to all the bidders, without the profile there couldn’t be an auction all users would essentially be equal in value. The profile is what is known as the audience taxonomy, you can look it up, it shows the type of data typically collected.
It does contain some personal information, but the waste majority is purchase history and purchase intent. They don’t really care about you as a person, all they care about it how likely it is that you are going to make a purchase, that is what determines how valuable you are.