I agree that AI art often takes from artists’ work, which is valid. However, this isn't the case here. The game developer has stated that they can't spend money to commission art at this stage of development, I assume their focus is on gameplay and the unique style they want to create. They’re choosing AI-generated art because it allows them to maintain that unique style while keeping their costs manageable.
Saying, 'If you can rig a model, you can make a scene, and if you can make a scene, you can make an illustration for your card' oversimplifies the process. It's like saying, 'If you can drive a car, you can drive a bus, and if you can drive a bus, you can drive a truck.' In reality, each of those tasks requires different skills, time, and experience. Creating art for a game, especially when trying to maintain a unique style and updates, is a hard thing that can't always be replaced by an asset.
While free or paid assets are an option, they often don’t offer the flexibility or originality that a developer might need to create something distinct. AI art, while imperfect, can provide a compromise in this situation