I do not understand how people at these advertising agencies are so bad at their actual jobs.
I used to work in an advertising agency, the job is done by humans who go home and watch TV and play video games and generally interact with the rest of the human race on a fairly regular basis. There's no way in hell that they failed to register the public's dissatisfaction with AI. So how do they then sit in a pitch meeting and recommend its use?
I guarantee what happened here is that McDonald's wanted things to be cheap and so wanted to use AI, and the advertising agency just wanted to get McDonald's business so didn't push back on it as hard as they should have done. And look it's now done damage to their brand. They better come out with a statement real quick to clarify that it was McDonald's decision and not theirs, otherwise clients are going to be concerned that they're trying to cut corners.
Part of the job is to tell clients when they're being unreasonable. There was a property developer that we worked with a lot and he was always trying to get us to do deceptive things such as using CGI shots of his housing estate rather than the actual shots because the properties didn't look anything like what was being depicted in the CGI shots. I'm sure if we were doing it today he would be trying to use AI as well. Fortunately my boss was always able to talk him out of these decisions pointing out that it would simply result in him getting a reputation for dishonesty, and would in the long term hurt him.