I explored this space in depth a while back. The problem with approaching the creative side of advertising is that it's an arms race. There's a reason creative agencies don't work with clients that compete with each other: you cannot share what worked for one client with another, otherwise it becomes less effective for both. Once you find a formula that works, everyone copies it, and it's no longer useful (i.e ad blindness). You can treat this as an optimization problem, but then everyone will do the same. Those who stand out will be doing something different, using different methods to draw attention that is not automatable.

Also, there's usually not enough data available for making very good decisions, especially if it's based on longer but better signals of ROI, such as LTV or sale conversions. A long sales cycle means you might not have data for optimization until 60 days later.

Finally, another problem is that AI can lead to deceptive or manipulative design (think dark patterns on steroids). That isn't just an ethics problem, it's a problem that could lead to lawsuits (e.g. false advertising, advertising the wrong things to protected classes of people, etc)

In general, it's hard to optimize problems which involve others optimizing against you.