I didn't know this was a thing. Google chose that ad placement? Does it vary from viewer to viewer (eg. does your page look different than mine?).

How much is the per-view income from a site that does that? This explains why a lot of crappy sites look like that - handing over control to google to maximize ad revenue income causes google algos to optimize to some maxima of low-denominator quality. Who would intentionally place full-screen ads, after all!?