That's the sticking point for a lot of people (me included), it takes far more work to mock up a lookalike or ask a program to generate an image, when it's all just meant to be "something goes here," and is supposed to be easily identifiable for replacement. Same thing with placeholder text - we've had lorem ipsum for thirty years. The whole point of placeholders is to be obvious and easy to make and replace.

The most uncharitable read is that, in Clair Obscur's case, it was just some little posters on the wall that you'd never pay attention to, so they used AI shit to just get it done, and then when they got called out, they replaced it with something an artist made (or something better generated). At best, some artists were using the generated images as placeholders to help match the vibe, and missed replacing one with their actual work, but that is still incredibly irresponsible for both in the reasons above that make it easy to miss, and for using the plagiarism machine.