They can and they do, that's what ad networks are. There are plenty of ways to group sites by category and readership without individual targeting but middlemen add percentage costs to the ad spend which the industry has been slowly pushing out.
The bigger issue is that fine-grained targeting is still wanted so if you remove 3rd-party tracking then advertisers will go towards the biggest sites that can supply it via their own 1st-party tracking. Even then it's still hard to work with many vendors so even more of the money is now going to Google and Facebook who can just do it all with better data than anyone else.
