Automated ad fraud is why. It's the biggest problem you've never heard of.

The last time I heard it cited (which, to be fair, was a few years back) the actual number was 33%—for every three dollars spent on digital advertising, a dollar gets lost to fraud. Not too far off.

I had to disable Google display ads because 90+% was fraud

how did you know?

How old is that information? If I recall correctly, some of the big ad fraud rings were taken to court, and that killed the business model.

Roughly three years old I think. But if you're referring to the same ad fraud rings I'm thinking of: yeah, a few did get shut down (which iirc was a first) but there's plenty of new operations taking their place. Ad fraud is a relatively cheap way to make money if you can scale up your operation, and most perpetrators don't get caught or punished. Although that may change in the future.