Also entirely possible that the balance of the 400k websites account for a miniscule percentage of impressions.
What other things should the article show "hasn't happened"? That will be quite a big list.
As the OP says, it's odd that people lean towards "everything is A-OK!". I guess there are many, many jobs that rely on the ad-tech bubble sustaining itself.
"Of the 400,000 web addresses JPMorgan’s ads showed up on in a recent 30-day period, said Ms. Lemkau, only 12,000, or 3 percent, led to activity beyond an impression."