I use Brave. I have the rewards enabled.
When you open a new tab, does it not show an ad for you as the wallpaper of the new tab? I thought that space would show an ad regardless of rewards are on or off.
The ads that I get that I know are because of rewards is the desktop notifications that it pushes, that you can click on. Only ever clicked on a couple of them at most I think, but still have them enabled because I think the idea of Brave rewards and BAT is interesting.
Also, I no longer remember but, when you install Brave it does ask whether you want to enable Brave rewards or not, didn’t it? In which case I think at least some people might be clicking yes without meaning to/understanding. But in my case it was intentional anyways.