If I'm reading reviews about a certain product category, it's a fair bet I might be in the market for such a product. So the site could show me relevant ads.
If I'm reading a site devoted to a particular topic or activity, the publisher might reasonably guess that I could be in the market for related products, and offer relevant ads.
None of this requires any privacy-invasive tracking.
If I'm reading a general news site, the site shouldn't have any more idea what I'm "in the market for" than the publisher of a print newspaper I might buy.
If I'm browsing used-car listings, the site shouldn't have any idea what genre of novels I like to read, what my grocery cart usually contains, where I go to work out, or how many pets I have. Why does anyone think it's OK for a company to surreptitiously gather that sort of personal information about everyone?
Vogue subscribers are probably in the market for new designer clothes. People who watch Cesar Milan are probably in the market for pet supplies. Someone driving down a highway is probably in the market for gas and a snack. Someone who searches for “affordable laptop” is probably in the market to buy a new computer.
You don’t need to track someone’s every move to serve them relevant ads.