Every single ad seller's been caught by companies selling these dangerous ads. Google, yahoo, etc. They usually catch it within 3-5 days. That's too long.

In short, yes. Advertisements are a huge way to get malware onto people’s computers. This just one random article from a google search for “malware advertising” but there are tons and it still happens today.

https://arstechnica.com/information-technology/2016/03/big-n...

What is in the interest of the ad networks is income and plausible deniability.

“Sorry we didn’t realise that there was malicious content in that ad, we’ll do better in the future, and we’ll also work on taking less than four days to remove malicious content.”

In the meantime the reason ads are being bought is the ability to deploy customer enrichment experiences (the new name for malware) which will help customers better discover your product (by redirecting their browser, or rewriting links).

Are there ad networks that don't?

I have seen ads trigger site redirects, app download redirect to app stores etc. and even initiate apk(Android app package) file downloads automatically.