Why don't websites propose to host the ads instead? That way they can hardly be avoided (I think?), and users can't really complain about being tracked unless

Why don't websites propose to host the ads instead? That way they can hardly be avoided (I think?), and users can't really complain about being tracked unless the websites really use something that tracks their users. I would guess advertisers really want to track users, and they want to check if websites really display those ads, but they just could check at random.