It could well be naive A/B testing. "Oh, this configuration has really increased our click-through rates", not realising that it's because people are trying to click on something, and an ad jumps into the space that they're just about to click.
I honestly think that's the truth for the majority of cases like this, or at worst a kind of willful blindness. Of course there are the scammers, but I think they generally produce such terrible work that very few people use it on an ongoing basis. I'm sure there are examples between those two, but I reckon they're few and far between.
