Before cookie banners were required, do you think the average user would have any idea how many sites were tracking them? I don't think they did. It's beneficial if only to increase public awareness, because tracking is otherwise invisible.

Heck, I'm a reasonably technical user, and I wouldn't have noticed in most cases. Again, invisible. Now I have a negative first impression of a site if it annoys me with cookie banners, and a more positive one if not.