[hagbardgroup]

They do. Google also produces the most widely-used ad platform for publishers, which makes it much easier for those publishers to blacklist and whitelist given ads and advertisers.

The ads suck for a lot of reasons, but lack of capacity to filter them isn't one of them.

Plenty of ad units that you see on a publisher may be filled by Adsense on one pageview and by another ad network in another one. Those networks may or may not have the same quality requirements that Adsense does.

Publishers tend to optimize for the amount of money they can make from an ad rather than how good it looks. An ad ops person will filter out offensive or porny ads while otherwise looking to top out their commission pay.

They also give some control over how the text ads appear in terms of color and font: https://support.google.com/adsense/answer/6002607?hl=en

It's just that a lot of publishers don't know how to handle the settings or don't care. Most publishers are not tech-first companies, and their websites don't make the bulk of their revenue anyway. For any TV channel, their website is a rounding error in terms of total revenue.