That would be anti-competitive by Google. These are different ad networks, not advertisers. Ad networks need to be able to do their own attribution and click spam detection.

You missed the question.

Why allow any thing on any advertisement, regardless of network, that is not image or text? Anything else opens up security issues.

He just told you?

"Ad networks need to be able to do their own attribution and click spam detection."

This doesn't answer why the end product (the person receiving the ad) is exposed to anything but images and text, which was the question.

Step outside technical approach mode and look at it from the highest level possible -- why are end users ever given more than images and text, or, why are ads anything more than a very simple a href tag.

Spam detection and other protection of the ad platform should be done long before this information ever goes to the eyeball product owners.

No - spam protection needs as many signals as possible, sadly.

You will have headless browsers simulating clicks and so on. This gets extremely hard over time fake, and the more signals there are, the easier it's to spot anomalies.

In a way, the thinking is - a malicious actor will get at least a few of those signals inorganic and ML can detect them...

"Long before the information ever goes to the eyeball" => wish it was true.