Who would run a browser specifically designed to track and show ads? I can't imagine it ever being enough to support the ecosystem. Edit: And how is the locally gathered "attention" monitoring not exploitable by the people who get paid for the attention? Running a bunch of VMs that "pay attention" to the ad seems like a cheap thing to rig up.
Yeah, I don't understand Chrome users either.
> Edit:
People already do this with mixed success. There's also nothing stopping you from modifying the browser falsely report that the user actually viewed the ads.