Attack ads reflect the actual behaviour of a person, actual footage etc. Image generation doesn't.

So the problem isn't that it's too real; it's that it's not real enough.

When the phrase whataboutism first became popular I really disliked it, but now that the idea is in my head I see things like this post constantly.

The law protects certain uses of things like copyright because the societal benefit outweighs any real cost, political opponents being able to use each others likeness in an ad is not nearly the same as a company getting the use of a celebrity without paying for it.

And please don't start with the "attack ads harm society", you chose to limit your description to attack ads when what you really meant was political ads (attacking or otherwise).

For the same reason the news exists.

CBS News is allowed to show footage of ScarJo speaking at a charity event within its newscast.

They're not allowed to use ScarJo's image with a caption saying "I trust CBS" on a billboard promoting CBS News.

Attack ads are part of political discourse, like the news. They're not being used to sell sneakers or cars.