you still get to display an advertisement. so it isn't "mined BTC > $1 --> success"; it is "mined BTC + expected value of running scam ad > $1 --> success"
I think his point was a hypothetical without the advertising component. Like if they just embedded bitcoin miners in every page that displayed a youtube video.
PS: Also, I wonder what other sites could be affected. Requirement is "user spending a lot of time on a page", so maybe blogging services with long posts, or shady sites with online sports broadcasts. Ugh, adblocker slowly becomes a requirement for modern web.
